💾 Archived View for gemini.bortzmeyer.org › rfc-mirror › rfc6386.txt captured on 2022-07-16 at 19:26:59.
⬅️ Previous capture (2021-11-30)
-=-=-=-=-=-=-
Independent Submission J. Bankoski
Request for Comments: 6386 J. Koleszar
Category: Informational L. Quillio
ISSN: 2070-1721 J. Salonen
P. Wilkins
Y. Xu
Google Inc.
November 2011
VP8 Data Format and Decoding Guide
Abstract
This document describes the VP8 compressed video data format,
together with a discussion of the decoding procedure for the format.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
This is a contribution to the RFC Series, independently of any other
RFC stream. The RFC Editor has chosen to publish this document at
its discretion and makes no statement about its value for
implementation or deployment. Documents approved for publication by
the RFC Editor are not a candidate for any level of Internet
Standard; see Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc6386.
Copyright Notice
Copyright (c) 2011 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document.
Bankoski, et al. Informational [Page 1]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
Table of Contents
1. Introduction ....................................................4
2. Format Overview .................................................5
3. Compressed Frame Types ..........................................7
4. Overview of Compressed Data Format ..............................8
5. Overview of the Decoding Process ................................9
6. Description of Algorithms ......................................14
7. Boolean Entropy Decoder ........................................16
7.1. Underlying Theory of Coding ...............................17
7.2. Practical Algorithm Description ...........................18
7.3. Actual Implementation .....................................20
8. Compressed Data Components .....................................25
8.1. Tree Coding Implementation ................................27
8.2. Tree Coding Example .......................................28
9. Frame Header ...................................................30
9.1. Uncompressed Data Chunk ...................................30
9.2. Color Space and Pixel Type (Key Frames Only) ..............33
9.3. Segment-Based Adjustments .................................34
9.4. Loop Filter Type and Levels ...............................35
9.5. Token Partition and Partition Data Offsets ................36
9.6. Dequantization Indices ....................................37
9.7. Refresh Golden Frame and Altref Frame .....................38
9.8. Refresh Last Frame Buffer .................................39
9.9. DCT Coefficient Probability Update ........................39
9.10. Remaining Frame Header Data (Non-Key Frame) ..............40
9.11. Remaining Frame Header Data (Key Frame) ..................41
10. Segment-Based Feature Adjustments .............................41
11. Key Frame Macroblock Prediction Records .......................42
11.1. mb_skip_coeff ............................................42
11.2. Luma Modes ...............................................42
11.3. Subblock Mode Contexts ...................................45
11.4. Chroma Modes .............................................46
11.5. Subblock Mode Probability Table ..........................47
12. Intraframe Prediction .........................................50
12.1. mb_skip_coeff ............................................51
12.2. Chroma Prediction ........................................51
12.3. Luma Prediction ..........................................54
13. DCT Coefficient Decoding ......................................60
13.1. Macroblock without Non-Zero Coefficient Values ...........61
13.2. Coding of Individual Coefficient Values ..................61
13.3. Token Probabilities ......................................63
13.4. Token Probability Updates ................................68
13.5. Default Token Probability Table ..........................73
Bankoski, et al. Informational [Page 2]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
14. DCT and WHT Inversion and Macroblock Reconstruction ...........76
14.1. Dequantization ...........................................76
14.2. Inverse Transforms .......................................78
14.3. Implementation of the WHT Inversion ......................78
14.4. Implementation of the DCT Inversion ......................81
14.5. Summation of Predictor and Residue .......................83
15. Loop Filter ...................................................84
15.1. Filter Geometry and Overall Procedure ....................85
15.2. Simple Filter ............................................87
15.3. Normal Filter ............................................91
15.4. Calculation of Control Parameters ........................95
16. Interframe Macroblock Prediction Records ......................97
16.1. Intra-Predicted Macroblocks ..............................97
16.2. Inter-Predicted Macroblocks ..............................98
16.3. Mode and Motion Vector Contexts ..........................99
16.4. Split Prediction ........................................105
17. Motion Vector Decoding .......................................108
17.1. Coding of Each Component ................................108
17.2. Probability Updates .....................................110
18. Interframe Prediction ........................................113
18.1. Bounds on, and Adjustment of, Motion Vectors ............113
18.2. Prediction Subblocks ....................................115
18.3. Sub-Pixel Interpolation .................................115
18.4. Filter Properties .......................................118
19. Annex A: Bitstream Syntax ....................................120
19.1. Uncompressed Data Chunk .................................121
19.2. Frame Header ............................................122
19.3. Macroblock Data .........................................130
20. Attachment One: Reference Decoder Source Code ................133
20.1. bit_ops.h ...............................................133
20.2. bool_decoder.h ..........................................133
20.3. dequant_data.h ..........................................137
20.4. dixie.c .................................................138
20.5. dixie.h .................................................151
20.6. dixie_loopfilter.c ......................................158
20.7. dixie_loopfilter.h ......................................170
20.8. idct_add.c ..............................................171
20.9. idct_add.h ..............................................174
20.10. mem.h ..................................................175
20.11. modemv.c ...............................................176
20.12. modemv.h ...............................................192
20.13. modemv_data.h ..........................................193
20.14. predict.c ..............................................198
20.15. predict.h ..............................................231
20.16. tokens.c ...............................................232
20.17. tokens.h ...............................................242
20.18. vp8_prob_data.h ........................................243
20.19. vpx_codec_internal.h ...................................252
Bankoski, et al. Informational [Page 3]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
20.20. vpx_decoder.h ..........................................263
20.21. vpx_decoder_compat.h ...................................271
20.22. vpx_image.c ............................................285
20.23. vpx_image.h ............................................291
20.24. vpx_integer.h ..........................................298
20.25. AUTHORS File ...........................................299
20.26. LICENSE ................................................301
20.27. PATENTS ................................................302
21. Security Considerations ......................................302
22. References ...................................................303
22.1. Normative Reference .....................................303
22.2. Informative References ..................................303
1. Introduction
This document describes the VP8 compressed video data format,
together with a discussion of the decoding procedure for the format.
It is intended to be used in conjunction with, and as a guide to, the
reference decoder source code provided in Attachment One
(Section 20). If there are any conflicts between this narrative and
the reference source code, the reference source code should be
considered correct. The bitstream is defined by the reference source
code and not this narrative.
Like many modern video compression schemes, VP8 is based on
decomposition of frames into square subblocks of pixels, prediction
of such subblocks using previously constructed blocks, and adjustment
of such predictions (as well as synthesis of unpredicted blocks)
using a discrete cosine transform (hereafter abbreviated as DCT). In
one special case, however, VP8 uses a Walsh-Hadamard transform
(hereafter abbreviated as WHT) instead of a DCT.
Roughly speaking, such systems reduce datarate by exploiting the
temporal and spatial coherence of most video signals. It is more
efficient to specify the location of a visually similar portion of a
prior frame than it is to specify pixel values. The frequency
segregation provided by the DCT and WHT facilitates the exploitation
of both spatial coherence in the original signal and the tolerance of
the human visual system to moderate losses of fidelity in the
reconstituted signal.
VP8 augments these basic concepts with, among other things,
sophisticated usage of contextual probabilities. The result is a
significant reduction in datarate at a given quality.
Bankoski, et al. Informational [Page 4]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
Unlike some similar schemes (the older MPEG formats, for example),
VP8 specifies exact values for reconstructed pixels. Specifically,
the specification for the DCT and WHT portions of the reconstruction
does not allow for any "drift" caused by truncation of fractions.
Rather, the algorithm is specified using fixed-precision integer
operations exclusively. This greatly facilitates the verification of
the correctness of a decoder implementation and also avoids
difficult-to-predict visual incongruities between such
implementations.
It should be remarked that, in a complete video playback system, the
displayed frames may or may not be identical to the reconstructed
frames. Many systems apply a final level of filtering (commonly
referred to as postprocessing) to the reconstructed frames prior to
viewing. Such postprocessing has no effect on the decoding and
reconstruction of subsequent frames (which are predicted using the
completely specified reconstructed frames) and is beyond the scope of
this document. In practice, the nature and extent of this sort of
postprocessing is dependent on both the taste of the user and on the
computational facilities of the playback environment.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
2. Format Overview
VP8 works exclusively with an 8-bit YUV 4:2:0 image format. In this
format, each 8-bit pixel in the two chroma planes (U and V)
corresponds positionally to a 2x2 block of 8-bit luma pixels in the
Y plane; coordinates of the upper left corner of the Y block are of
course exactly twice the coordinates of the corresponding chroma
pixels. When we refer to pixels or pixel distances without
specifying a plane, we are implicitly referring to the Y plane or to
the complete image, both of which have the same (full) resolution.
As is usually the case, the pixels are simply a large array of bytes
stored in rows from top to bottom, each row being stored from left to
right. This "left to right" then "top to bottom" raster-scan order
is reflected in the layout of the compressed data as well.
Provision has been made in the VP8 bitstream header for the support
of a secondary YUV color format, in the form of a reserved bit.
Occasionally, at very low datarates, a compression system may decide
to reduce the resolution of the input signal to facilitate efficient
compression. The VP8 data format supports this via optional
upscaling of its internal reconstruction buffer prior to output (this
Bankoski, et al. Informational [Page 5]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
is completely distinct from the optional postprocessing discussed
earlier, which has nothing to do with decoding per se). This
upsampling restores the video frames to their original resolution.
In other words, the compression/decompression system can be viewed as
a "black box", where the input and output are always at a given
resolution. The compressor might decide to "cheat" and process the
signal at a lower resolution. In that case, the decompressor needs
the ability to restore the signal to its original resolution.
Internally, VP8 decomposes each output frame into an array of
macroblocks. A macroblock is a square array of pixels whose Y
dimensions are 16x16 and whose U and V dimensions are 8x8.
Macroblock-level data in a compressed frame occurs (and must be
processed) in a raster order similar to that of the pixels comprising
the frame.
Macroblocks are further decomposed into 4x4 subblocks. Every
macroblock has 16 Y subblocks, 4 U subblocks, and 4 V subblocks. Any
subblock-level data (and processing of such data) again occurs in
raster order, this time in raster order within the containing
macroblock.
As discussed in further detail below, data can be specified at the
levels of both macroblocks and their subblocks.
Pixels are always treated, at a minimum, at the level of subblocks,
which may be thought of as the "atoms" of the VP8 algorithm. In
particular, the 2x2 chroma blocks corresponding to 4x4 Y subblocks
are never treated explicitly in the data format or in the algorithm
specification.
The DCT and WHT always operate at a 4x4 resolution. The DCT is used
for the 16Y, 4U, and 4V subblocks. The WHT is used (with some but
not all prediction modes) to encode a 4x4 array comprising the
average intensities of the 16 Y subblocks of a macroblock. These
average intensities are, up to a constant normalization factor,
nothing more than the 0th DCT coefficients of the Y subblocks. This
"higher-level" WHT is a substitute for the explicit specification of
those coefficients, in exactly the same way as the DCT of a subblock
substitutes for the specification of the pixel values comprising the
subblock. We consider this 4x4 array as a second-order subblock
called Y2, and think of a macroblock as containing 24 "real"
subblocks and, sometimes, a 25th "virtual" subblock. This is dealt
with further in Section 13.
The frame layout used by the reference decoder may be found in the
file vpx_image.h (Section 20.23).
Bankoski, et al. Informational [Page 6]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
3. Compressed Frame Types
There are only two types of frames in VP8.
Intraframes (also called key frames and, in MPEG terminology,
I-frames) are decoded without reference to any other frame in a
sequence; that is, the decompressor reconstructs such frames
beginning from its "default" state. Key frames provide random access
(or seeking) points in a video stream.
Interframes (also called prediction frames and, in MPEG terminology,
P-frames) are encoded with reference to prior frames, specifically
all prior frames up to and including the most recent key frame.
Generally speaking, the correct decoding of an interframe depends on
the correct decoding of the most recent key frame and all ensuing
frames. Consequently, the decoding algorithm is not tolerant of
dropped frames: In an environment in which frames may be dropped or
corrupted, correct decoding will not be possible until a key frame is
correctly received.
In contrast to MPEG, there is no use of bidirectional prediction. No
frame is predicted using frames temporally subsequent to it; there is
no analog to an MPEG B-frame.
Secondly, VP8 augments these notions with that of alternate
prediction frames, called golden frames and altref frames
(alternative reference frames). Blocks in an interframe may be
predicted using blocks in the immediately previous frame as well as
the most recent golden frame or altref frame. Every key frame is
automatically golden and altref, and any interframe may optionally
replace the most recent golden or altref frame.
Golden frames and altref frames may also be used to partially
overcome the intolerance to dropped frames discussed above: If a
compressor is configured to code golden frames only with reference to
the prior golden frame (and key frame), then the "substream" of key
and golden frames may be decoded regardless of loss of other
interframes. Roughly speaking, the implementation requires (on the
compressor side) that golden frames subsume and recode any context
updates effected by the intervening interframes. A typical
application of this approach is video conferencing, in which
retransmission of a prior golden frame and/or a delay in playback
until receipt of the next golden frame is preferable to a larger
retransmit and/or delay until the next key frame.
Bankoski, et al. Informational [Page 7]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
4. Overview of Compressed Data Format
The input to a VP8 decoder is a sequence of compressed frames whose
order matches their order in time. Issues such as the duration of
frames, the corresponding audio, and synchronization are generally
provided by the playback environment and are irrelevant to the
decoding process itself; however, to aid in fast seeking, a start
code is included in the header of each key frame.
The decoder is simply presented with a sequence of compressed frames
and produces a sequence of decompressed (reconstructed) YUV frames
corresponding to the input sequence. As stated in the Introduction,
the exact pixel values in the reconstructed frame are part of VP8's
specification. This document specifies the layout of the compressed
frames and gives unambiguous algorithms for the correct production of
reconstructed frames.
The first frame presented to the decompressor is of course a key
frame. This may be followed by any number of interframes; the
correct reconstruction of each frame depends on all prior frames up
to the key frame. The next key frame restarts this process: The
decompressor resets to its default initial condition upon reception
of a key frame, and the decoding of a key frame (and its ensuing
interframes) is completely independent of any prior decoding.
At the highest level, every compressed frame has three or more
pieces. It begins with an uncompressed data chunk comprising
10 bytes in the case of key frames and 3 bytes for interframes. This
is followed by two or more blocks of compressed data (called
partitions). These compressed data partitions begin and end on byte
boundaries.
The first compressed partition has two subsections:
1. Header information that applies to the frame as a whole.
2. Per-macroblock information specifying how each macroblock is
predicted from the already-reconstructed data that is available
to the decompressor.
As stated above, the macroblock-level information occurs in raster-
scan order.
The rest of the partitions contain, for each block, the DCT/WHT
coefficients (quantized and logically compressed) of the residue
signal to be added to the predicted block values. It typically
accounts for roughly 70% of the overall datarate. VP8 supports
packing the compressed DCT/WHT coefficients' data from macroblock
Bankoski, et al. Informational [Page 8]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
rows into separate partitions. If there is more than one partition
for these coefficients, the sizes of the partitions -- except the
last partition -- in bytes are also present in the bitstream right
after the above first partition. Each of the sizes is a 3-byte data
item written in little endian format. These sizes provide the
decoder direct access to all DCT/WHT coefficient partitions, which
enables parallel processing of the coefficients in a decoder.
The separate partitioning of the prediction data and coefficient data
also allows flexibility in the implementation of a decompressor: An
implementation may decode and store the prediction information for
the whole frame and then decode, transform, and add the residue
signal to the entire frame, or it may simultaneously decode both
partitions, calculating prediction information and adding in the
residue signal for each block in order. The length field in the
frame tag, which allows decoding of the second partition to begin
before the first partition has been completely decoded, is necessary
for the second "block-at-a-time" decoder implementation.
All partitions are decoded using separate instances of the boolean
entropy decoder described in Section 7. Although some of the data
represented within the partitions is conceptually "flat" (a bit is
just a bit with no probabilistic expectation one way or the other),
because of the way such coders work, there is never a direct
correspondence between a "conceptual bit" and an actual physical bit
in the compressed data partitions. Only in the 3- or 10-byte
uncompressed chunk described above is there such a physical
correspondence.
A related matter is that seeking within a partition is not supported.
The data must be decompressed and processed (or at least stored) in
the order in which it occurs in the partition.
While this document specifies the ordering of the partition data
correctly, the details and semantics of this data are discussed in a
more logical fashion to facilitate comprehension. For example, the
frame header contains updates to many probability tables used in
decoding per-macroblock data. The per-macroblock data is often
described before the layouts of the probabilities and their updates,
even though this is the opposite of their order in the bitstream.
5. Overview of the Decoding Process
A VP8 decoder needs to maintain four YUV frame buffers whose
resolutions are at least equal to that of the encoded image. These
buffers hold the current frame being reconstructed, the immediately
previous reconstructed frame, the most recent golden frame, and the
most recent altref frame.
Bankoski, et al. Informational [Page 9]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
Most implementations will wish to "pad" these buffers with
"invisible" pixels that extend a moderate number of pixels beyond all
four edges of the visible image. This simplifies interframe
prediction by allowing all (or most) prediction blocks -- which are
not guaranteed to lie within the visible area of a prior frame -- to
address usable image data.
Regardless of the amount of padding chosen, the invisible rows above
(or below) the image are filled with copies of the top (or bottom)
row of the image; the invisible columns to the left (or right) of the
image are filled with copies of the leftmost (or rightmost) visible
row; and the four invisible corners are filled with copies of the
corresponding visible corner pixels. The use of these prediction
buffers (and suggested sizes for the halo) will be elaborated on in
the discussion of motion vectors, interframe prediction, and
sub-pixel interpolation later in this document.
As will be seen in the description of the frame header, the image
dimensions are specified (and can change) with every key frame.
These buffers (and any other data structures whose size depends on
the size of the image) should be allocated (or re-allocated)
immediately after the dimensions are decoded.
Leaving most of the details for later elaboration, the following is
an outline of the decoding process.
First, the frame header (the beginning of the first data partition)
is decoded. Altering or augmenting the maintained state of the
decoder, this provides the context in which the per-macroblock data
can be interpreted.
The macroblock data occurs (and must be processed) in raster-scan
order. This data comes in two or more parts. The first (prediction
or mode) part comes in the remainder of the first data partition.
The other parts comprise the data partition(s) for the DCT/WHT
coefficients of the residue signal. For each macroblock, the
prediction data must be processed before the residue.
Each macroblock is predicted using one (and only one) of four
possible frames. All macroblocks in a key frame, and all intra-coded
macroblocks in an interframe, are predicted using the already-decoded
macroblocks in the current frame. Macroblocks in an interframe may
also be predicted using the previous frame, the golden frame, or the
altref frame. Such macroblocks are said to be inter-coded.
Bankoski, et al. Informational [Page 10]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
The purpose of prediction is to use already-constructed image data to
approximate the portion of the original image being reconstructed.
The effect of any of the prediction modes is then to write a
macroblock-sized prediction buffer containing this approximation.
Regardless of the prediction method, the residue DCT signal is
decoded, dequantized, reverse-transformed, and added to the
prediction buffer to produce the (almost final) reconstruction value
of the macroblock, which is stored in the correct position of the
current frame buffer.
The residue signal consists of 24 (sixteen Y, four U, and four V) 4x4
quantized and losslessly compressed DCT transforms approximating the
difference between the original macroblock in the uncompressed source
and the prediction buffer. For most prediction modes, the 0th
coefficients of the sixteen Y subblocks are expressed via a 25th WHT
of the second-order virtual Y2 subblock discussed above.
Intra-prediction exploits the spatial coherence of frames. The 16x16
luma (Y) and 8x8 chroma (UV) components are predicted independently
of each other using one of four simple means of pixel propagation,
starting from the already-reconstructed (16-pixel-long luma, 8-pixel-
long chroma) row above, and column to the left of, the current
macroblock. The four methods are:
1. Copying the row from above throughout the prediction buffer.
2. Copying the column from the left throughout the prediction
buffer.
3. Copying the average value of the row and column throughout the
prediction buffer.
4. Extrapolation from the row and column using the (fixed) second
difference (horizontal and vertical) from the upper left corner.
Additionally, the sixteen Y subblocks may be predicted independently
of each other using one of ten different modes, four of which are 4x4
analogs of those described above, augmented with six "diagonal"
prediction methods. There are two types of predictions, one intra
and one prediction (among all the modes), for which the residue
signal does not use the Y2 block to encode the DC portion of the
sixteen 4x4 Y subblock DCTs. This "independent Y subblock" mode has
no effect on the 8x8 chroma prediction.
Bankoski, et al. Informational [Page 11]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
Inter-prediction exploits the temporal coherence between nearby
frames. Except for the choice of the prediction frame itself, there
is no difference between inter-prediction based on the previous frame
and that based on the golden frame or altref frame.
Inter-prediction is conceptually very simple. While, for reasons of
efficiency, there are several methods of encoding the relationship
between the current macroblock and corresponding sections of the
prediction frame, ultimately each of the sixteen Y subblocks is
related to a 4x4 subblock of the prediction frame, whose position in
that frame differs from the current subblock position by a (usually
small) displacement. These two-dimensional displacements are called
motion vectors.
The motion vectors used by VP8 have quarter-pixel precision.
Prediction of a subblock using a motion vector that happens to have
integer (whole number) components is very easy: The 4x4 block of
pixels from the displaced block in the previous, golden, or altref
frame is simply copied into the correct position of the current
macroblock's prediction buffer.
Fractional displacements are conceptually and implementationally more
complex. They require the inference (or synthesis) of sample values
that, strictly speaking, do not exist. This is one of the most basic
problems in signal processing, and readers conversant with that
subject will see that the approach taken by VP8 provides a good
balance of robustness, accuracy, and efficiency.
Leaving the details for the implementation discussion below, the
pixel interpolation is calculated by applying a kernel filter (using
reasonable-precision integer math) three pixels on either side, both
horizontally and vertically, of the pixel to be synthesized. The
resulting 4x4 block of synthetic pixels is then copied into position
exactly as in the case of integer displacements.
Each of the eight chroma subblocks is handled similarly. Their
motion vectors are never specified explicitly; instead, the motion
vector for each chroma subblock is calculated by averaging the
vectors of the four Y subblocks that occupy the same area of the
frame. Since chroma pixels have twice the diameter (and four times
the area) of luma pixels, the calculated chroma motion vectors have
1/8-pixel resolution, but the procedure for copying or generating
pixels for each subblock is essentially identical to that done in the
luma plane.
Bankoski, et al. Informational [Page 12]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
After all the macroblocks have been generated (predicted and
corrected with the DCT/WHT residue), a filtering step (the loop
filter) is applied to the entire frame. The purpose of the loop
filter is to reduce blocking artifacts at the boundaries between
macroblocks and between subblocks of the macroblocks. The term "loop
filter" is used because this filter is part of the "coding loop";
that is, it affects the reconstructed frame buffers that are used to
predict ensuing frames. This is distinguished from the
postprocessing filters discussed earlier, which affect only the
viewed video and do not "feed into" subsequent frames.
Next, if signaled in the data, the current frame may replace the
golden frame prediction buffer and/or the altref frame buffer.
The halos of the frame buffers are next filled as specified above.
Finally, at least as far as decoding is concerned, the (references
to) the "current" and "last" frame buffers should be exchanged in
preparation for the next frame.
Various processes may be required (or desired) before viewing the
generated frame. As discussed in the frame dimension information
below, truncation and/or upscaling of the frame may be required.
Some playback systems may require a different frame format (RGB,
YUY2, etc.). Finally, as mentioned in the Introduction, further
postprocessing or filtering of the image prior to viewing may be
desired. Since the primary purpose of this document is a decoding
specification, the postprocessing is not specified in this document.
While the basic ideas of prediction and correction used by VP8 are
straightforward, many of the details are quite complex. The
management of probabilities is particularly elaborate. Not only do
the various modes of intra-prediction and motion vector specification
have associated probabilities, but they, together with the coding of
DCT coefficients and motion vectors, often base these probabilities
on a variety of contextual information (calculated from what has been
decoded so far), as well as on explicit modification via the frame
header.
The "top-level" of decoding and frame reconstruction is implemented
in the reference decoder file dixie.c (Section 20.4).
This concludes our summary of decoding and reconstruction; we
continue by discussing the individual aspects in more depth.
A reasonable "divide and conquer" approach to implementation of a
decoder is to begin by decoding streams composed exclusively of key
frames. After that works reliably, interframe handling can be added
more easily than if complete functionality were attempted
Bankoski, et al. Informational [Page 13]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
immediately. In accordance with this, we first discuss components
needed to decode key frames (most of which are also used in the
decoding of interframes) and conclude with topics exclusive to
interframes.
6. Description of Algorithms
As the intent of this document, together with the reference decoder
source code, is to specify a platform-independent procedure for the
decoding and reconstruction of a VP8 video stream, many (small)
algorithms must be described exactly.
Due to its near-universality, terseness, ability to easily describe
calculation at specific precisions, and the fact that On2's reference
VP8 decoder is written in C, these algorithm fragments are written
using the C programming language, augmented with a few simple
definitions below.
The standard (and best) reference for C is [Kernighan].
Many code fragments will be presented in this document. Some will be
nearly identical to corresponding sections of the reference decoder;
others will differ. Roughly speaking, there are three reasons for
such differences:
1. For reasons of efficiency, the reference decoder version may be
less obvious.
2. The reference decoder often uses large data structures to
maintain context that need not be described or used here.
3. The authors of this document felt that a different expression of
the same algorithm might facilitate exposition.
Regardless of the chosen presentation, the calculation effected by
any of the algorithms described here is identical to that effected by
the corresponding portion of the reference decoder.
All VP8 decoding algorithms use integer math. To facilitate
specification of arithmetic precision, we define the following types.
---- Begin code block --------------------------------------
typedef signed char int8; /* signed int exactly 8 bits wide */
typedef unsigned char uint8; /* unsigned "" */
typedef short int16; /* signed int exactly 16 bits wide */
typedef unsigned int16 uint16; /* unsigned "" */
Bankoski, et al. Informational [Page 14]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/* int32 is a signed integer type at least 32 bits wide */
typedef long int32; /* guaranteed to work on all systems */
typedef int int32; /* will be more efficient on some systems */
typedef unsigned int32 uint32;
/* unsigned integer type, at least 16 bits wide, whose exact size
is most convenient to whatever processor we are using */
typedef unsigned int uint;
/* While pixels themselves are 8-bit unsigned integers,
pixel arithmetic often occurs at 16- or 32-bit precision and
the results need to be "saturated" or clamped to an 8-bit
range. */
typedef uint8 Pixel;
Pixel clamp255(int32 v) { return v < 0? 0 : (v < 255? v : 255);}
/* As is elaborated in the discussion of the bool_decoder below,
VP8 represents probabilities as unsigned 8-bit numbers. */
typedef uint8 Prob;
---- End code block ----------------------------------------
We occasionally need to discuss mathematical functions involving
honest-to-goodness "infinite precision" real numbers. The DCT is
first described via the cosine function cos; the ratio of the lengths
of the circumference and diameter of a circle is denoted pi; at one
point, we take a (base 1/2) logarithm, denoted log; and pow(x, y)
denotes x raised to the power y. If x = 2 and y is a small
non-negative integer, pow(2, y) may be expressed in C as 1 << y.
Finally, we sometimes need to divide signed integers by powers of
two; that is, we occasionally right-shift signed numbers. The
behavior of such shifts (i.e., the propagation of the sign bit) is,
perhaps surprisingly, not defined by the C language itself and is
left up to individual compilers. Because of the utility of this
frequently needed operation, it is at least arguable that it should
be defined by the language (to naturally propagate the sign bit) and,
at a minimum, should be correctly implemented by any reasonable
compiler. In the interest of strict portability, we attempt to call
attention to these shifts when they arise.
Bankoski, et al. Informational [Page 15]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
7. Boolean Entropy Decoder
As discussed in the overview above, essentially the entire VP8 data
stream is encoded using a boolean entropy coder.
An understanding of the bool_decoder is critical to the
implementation of a VP8 decompressor, so we discuss the bool_decoder
in detail. It is easier to comprehend the bool_decoder in
conjunction with the bool_encoder used by the compressor to write the
compressed data partitions.
The bool_encoder encodes (and the bool_decoder decodes) one bool
(zero-or-one boolean value) at a time. Its purpose is to losslessly
compress a sequence of bools for which the probability of their being
zero or one can be well-estimated (via constant or previously coded
information) at the time they are written, using identical
corresponding probabilities at the time they are read.
As the reader is probably aware, if a bool is much more likely to be
zero than one (for instance), it can, on average, be faithfully
encoded using much less than one bit per value. The bool_encoder
exploits this.
In the 1940s, [Shannon] proved that there is a lower bound for the
average datarate of a faithful encoding of a sequence of bools (whose
probability distributions are known and are independent of each
other) and also that there are encoding algorithms that approximate
this lower bound as closely as one wishes.
If we encode a sequence of bools whose probability of being zero is p
(and whose probability of being 1 is 1-p), the lowest possible
datarate per value is
plog(p) + (1-p)log(1-p);
taking the logarithms to the base 1/2 expresses the datarate in bits/
value.
We give two simple examples. At one extreme, if p = 1/2, then log(p)
= log(1-p) = 1, and the lowest possible datarate per bool is 1/2 +
1/2 = 1; that is, we cannot do any better than simply literally
writing out bits. At another extreme, if p is very small, say p =
1/1024, then log(p)=10, log(1-p) is roughly .0014, and the lowest
possible datarate is approximately 10/1024 + .0014, roughly 1/100 of
a bit per bool.
Bankoski, et al. Informational [Page 16]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
Because most of the bools in the VP8 datastream have zero-
probabilities nowhere near 1/2, the compression provided by the
bool_encoder is critical to the performance of VP8.
The boolean coder used by VP8 is a variant of an arithmetic coder.
An excellent discussion of arithmetic coding (and other lossless
compression techniques) can be found in [Bell].
7.1. Underlying Theory of Coding
The basic idea used by the boolean coder is to consider the entire
data stream (either of the partitions in our case) as the binary
expansion of a single number x with 0 <= x < 1. The bits (or bytes)
in x are of course written from high to low order, and if b[j] (B[j])
is the j^(th) bit (byte) in the partition, the value x is simply the
sum (starting with j = 1) of pow(2, -j) * b[j] or pow(256, -j) *
B[j].
Before the first bool is coded, all values of x are possible.
The coding of each bool restricts the possible values of x in
proportion to the probability of what is coded. If p1 is the
probability of the first bool being zero and a zero is coded, the
range of possible values of x is restricted to 0 <= x < p1. If a one
is coded, the range becomes p1 <= x < 1.
The coding continues by repeating the same idea. At every stage,
there is an interval a <= x < b of possible values of x. If p is the
probability of a zero being coded at this stage and a zero is coded,
the interval becomes a <= x < a + (p(b-a)). If a one is coded, the
possible values of x are restricted to a + (p(b-a)) <= x < b.
Assuming that only finitely many values are to be coded, after the
encoder has received the last bool, it can write as its output any
value x that lies in the final interval. VP8 simply writes the left
endpoint of the final interval. Consequently, the output it would
make if encoding were to stop at any time either increases or stays
the same as each bool is encoded.
Decoding parallels encoding. The decoder is presented with the
number x, which has only the initial restriction 0 <= x < 1. To
decode the first bool, the decoder is given the first probability p1.
If x < p1, a zero is decoded; if x >= p1, a one is decoded. In
either case, the new restriction on x -- that is, the interval of
possible values of x -- is remembered.
Bankoski, et al. Informational [Page 17]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
Decoding continues in exactly the same way: If a <= x < b is the
current interval and we are to decode a bool with zero-probability p,
we return a zero if a <= x < a + (p(b-a)) and a one if a + (p(b-a))
<= x < b. In either case, the new restriction is remembered in
preparation for decoding the next bool.
The process outlined above uses real numbers of infinite precision to
express the probabilities and ranges. It is true that, if one could
actualize this process and coded a large number of bools whose
supplied probabilities matched their value distributions, the
datarate achieved would approach the theoretical minimum as the
number of bools encoded increased.
Unfortunately, computers operate at finite precision, and an
approximation to the theoretically perfect process described above is
necessary. Such approximation increases the datarate but, at quite
moderate precision and for a wide variety of data sets, this increase
is negligible.
The only conceptual limitations are, first, that coder probabilities
must be expressed at finite precision and, second, that the decoder
be able to detect each individual modification to the value interval
via examination of a fixed amount of input. As a practical matter,
many of the implementation details stem from the fact that the coder
can function using only a small "window" to incrementally read or
write the arbitrarily precise number x.
7.2. Practical Algorithm Description
VP8's boolean coder works with 8-bit probabilities p. The range of
such p is 0 <= p <= 255; the actual probability represented by p is
p/256. Also, the coder is designed so that decoding of a bool
requires no more than an 8-bit comparison, and so that the state of
both the encoder and decoder can be easily represented using a small
number of unsigned 16-bit integers.
The details are most easily understood if we first describe the
algorithm using bit-at-a-time input and output. Aside from the
ability to maintain a position in this bitstream and write/read bits,
the encoder also needs the ability to add 1 to the bits already
output; after writing n bits, adding 1 to the existing output is the
same thing as adding pow(2, -n) to x.
Bankoski, et al. Informational [Page 18]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
Together with the bit position, the encoder must maintain two
unsigned 8-bit numbers, which we call "bottom" and "range". Writing
w for the n bits already written and S = pow(2, - n - 8) for the
scale of the current bit position one byte out, we have the following
constraint on all future values v of w (including the final value
v = x):
w + ( S * bottom ) <= v < w + ( S * ( bottom + range ) )
Thus, appending bottom to the already-written bits w gives the left
endpoint of the interval of possible values, appending bottom + range
gives the right endpoint, and range itself (scaled to the current
output position) is the length of the interval.
So that our probabilistic encodings are reasonably accurate, we do
not let range vary by more than a factor of two: It stays within the
bounds 128 <= range <= 255.
The process for encoding a boolean value val whose probability of
being zero is prob / 256 -- and whose probability of being one is
( 256 - prob ) / 256 -- with 1 <= prob <= 255 is as follows.
Using an unsigned 16-bit multiply followed by an unsigned right
shift, we calculate an unsigned 8-bit split value:
split = 1 + (((range - 1) * probability)]] >> 8)
split is approximately ( prob / 256 ) * range and lies within the
bounds 1 <= split <= range - 1. These bounds ensure the correctness
of the decoding procedure described below.
If the incoming boolean val to be encoded is false, we leave the left
interval endpoint bottom alone and reduce range, replacing it by
split. If the incoming val is true, we move up the left endpoint to
bottom + split, propagating any carry to the already-written value w
(this is where we need the ability to add 1 to w), and reduce range
to range - split.
Regardless of the value encoded, range has been reduced and now has
the bounds 1 <= range <= 254. If range < 128, the encoder doubles it
and shifts the high-order bit out of bottom to the output as it also
doubles bottom, repeating this process one bit at a time until 128 <=
range <= 255. Once this is completed, the encoder is ready to accept
another bool, maintaining the constraints described above.
After encoding the last bool, the partition may be completed by
appending bottom to the bitstream.
Bankoski, et al. Informational [Page 19]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
The decoder mimics the state of the encoder. It maintains, together
with an input bit position, two unsigned 8-bit numbers, a range
identical to that maintained by the encoder and a value. Decoding
one bool at a time, the decoder (in effect) tracks the same left
interval endpoint as does the encoder and subtracts it from the
remaining input. Appending the unread portion of the bitstream to
the 8-bit value gives the difference between the actual value encoded
and the known left endpoint.
The decoder is initialized by setting range = 255 and reading the
first 16 input bits into value. The decoder maintains range and
calculates split in exactly the same way as does the encoder.
To decode a bool, it compares value to split; if value < split, the
bool is zero, and range is replaced with split. If value >= split,
the bool is one, range is replaced with range - split, and value is
replaced with value - split.
Again, range is doubled one bit at a time until it is at least 128.
The value is doubled in parallel, shifting a new input bit into the
bottom each time.
Writing Value for value together with the unread input bits and Range
for range extended indefinitely on the right by zeros, the condition
Value < Range is maintained at all times by the decoder. In
particular, the bits shifted out of value as it is doubled are always
zero.
7.3. Actual Implementation
The C code below gives complete implementations of the encoder and
decoder described above. While they are logically identical to the
"bit-at-a-time" versions, they internally buffer a couple of extra
bytes of the bitstream. This allows I/O to be done (more
practically) a byte at a time and drastically reduces the number of
carries the encoder has to propagate into the already-written data.
Another (logically equivalent) implementation may be found in the
reference decoder file bool_decoder.h (Section 20.2).
Bankoski, et al. Informational [Page 20]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
---- Begin code block --------------------------------------
/* Encoder first */
typedef struct {
uint8 *output; /* ptr to next byte to be written */
uint32 range; /* 128 <= range <= 255 */
uint32 bottom; /* minimum value of remaining output */
int bit_count; /* # of shifts before an output byte
is available */
} bool_encoder;
/* Must set initial state of encoder before writing any bools. */
void init_bool_encoder(bool_encoder *e, uint8 *start_partition)
{
e->output = start_partition;
e->range = 255;
e->bottom = 0;
e->bit_count = 24;
}
/* Encoding very rarely produces a carry that must be propagated
to the already-written output. The arithmetic guarantees that
the propagation will never go beyond the beginning of the
output. Put another way, the encoded value x is always less
than one. */
void add_one_to_output(uint8 *q)
{
while (*--q == 255)
*q = 0;
++*q;
}
/* Main function writes a bool_value whose probability of being
zero is (expected to be) prob/256. */
void write_bool(bool_encoder *e, Prob prob, int bool_value)
{
/* split is approximately (range * prob) / 256 and,
crucially, is strictly bigger than zero and strictly
smaller than range */
uint32 split = 1 + (((e->range - 1) * prob) >> 8);
Bankoski, et al. Informational [Page 21]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
if (bool_value) {
e->bottom += split; /* move up bottom of interval */
e->range -= split; /* with corresponding decrease in range */
} else
e->range = split; /* decrease range, leaving bottom alone */
while (e->range < 128)
{
e->range <<= 1;
if (e->bottom & (1 << 31)) /* detect carry */
add_one_to_output(e->output);
e->bottom <<= 1; /* before shifting bottom */
if (!--e->bit_count) { /* write out high byte of bottom ... */
*e->output++ = (uint8) (e->bottom >> 24);
e->bottom &= (1 << 24) - 1; /* ... keeping low 3 bytes */
e->bit_count = 8; /* 8 shifts until next output */
}
}
}
/* Call this function (exactly once) after encoding the last
bool value for the partition being written */
void flush_bool_encoder(bool_encoder *e)
{
int c = e->bit_count;
uint32 v = e->bottom;
if (v & (1 << (32 - c))) /* propagate (unlikely) carry */
add_one_to_output(e->output);
v <<= c & 7; /* before shifting remaining output */
c >>= 3; /* to top of internal buffer */
while (--c >= 0)
v <<= 8;
c = 4;
while (--c >= 0) { /* write remaining data, possibly padded */
*e->output++ = (uint8) (v >> 24);
v <<= 8;
}
}
Bankoski, et al. Informational [Page 22]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/* Decoder state exactly parallels that of the encoder.
"value", together with the remaining input, equals the
complete encoded number x less the left endpoint of the
current coding interval. */
typedef struct {
uint8 *input; /* pointer to next compressed data byte */
uint32 range; /* always identical to encoder's range */
uint32 value; /* contains at least 8 significant bits */
int bit_count; /* # of bits shifted out of
value, at most 7 */
} bool_decoder;
/* Call this function before reading any bools from the
partition. */
void init_bool_decoder(bool_decoder *d, uint8 *start_partition)
{
{
int i = 0;
d->value = 0; /* value = first 2 input bytes */
while (++i <= 2)
d->value = (d->value << 8) | *start_partition++;
}
d->input = start_partition; /* ptr to next byte to be read */
d->range = 255; /* initial range is full */
d->bit_count = 0; /* have not yet shifted out any bits */
}
/* Main function reads a bool encoded at probability prob/256,
which of course must agree with the probability used when the
bool was written. */
int read_bool(bool_decoder *d, Prob prob)
{
/* range and split are identical to the corresponding values
used by the encoder when this bool was written */
uint32 split = 1 + (((d->range - 1) * prob) >> 8);
uint32 SPLIT = split << 8;
int retval; /* will be 0 or 1 */
Bankoski, et al. Informational [Page 23]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
if (d->value >= SPLIT) { /* encoded a one */
retval = 1;
d->range -= split; /* reduce range */
d->value -= SPLIT; /* subtract off left endpoint of interval */
} else { /* encoded a zero */
retval = 0;
d->range = split; /* reduce range, no change in left endpoint */
}
while (d->range < 128) { /* shift out irrelevant value bits */
d->value <<= 1;
d->range <<= 1;
if (++d->bit_count == 8) { /* shift in new bits 8 at a time */
d->bit_count = 0;
d->value |= *d->input++;
}
}
return retval;
}
/* Convenience function reads a "literal", that is, a "num_bits"-
wide unsigned value whose bits come high- to low-order, with
each bit encoded at probability 128 (i.e., 1/2). */
uint32 read_literal(bool_decoder *d, int num_bits)
{
uint32 v = 0;
while (num_bits--)
v = (v << 1) + read_bool(d, 128);
return v;
}
/* Variant reads a signed number */
int32 read_signed_literal(bool_decoder *d, int num_bits)
{
int32 v = 0;
if (!num_bits)
return 0;
if (read_bool(d, 128))
v = -1;
while (--num_bits)
v = (v << 1) + read_bool(d, 128);
return v;
}
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 24]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
8. Compressed Data Components
At the lowest level, VP8's compressed data is simply a sequence of
probabilistically encoded bools. Most of this data is composed of
(slightly) larger semantic units fashioned from bools, which we
describe here.
We sometimes use these descriptions in C expressions within data
format specifications. In this context, they refer to the return
value of a call to an appropriate bool_decoder d, reading (as always)
from its current reference point.
+--------------+-------+--------------------------------------------+
| Call | Alt. | Return |
+--------------+-------+--------------------------------------------+
| Bool(p) | B(p) | Bool with probability p/256 of being 0. |
| | | Return value of read_bool(d, p). |
| | | |
| Flag | F | A one-bit flag (same thing as a B(128) or |
| | | an L(1)). Abbreviated F. Return value of |
| | | read_bool(d, 128). |
| | | |
| Lit(n) | L(n) | Unsigned n-bit number encoded as n flags |
| | | (a "literal"). Abbreviated L(n). The |
| | | bits are read from high to low order. |
| | | Return value of read_literal(d, n). |
| | | |
| SignedLit(n) | | Signed n-bit number encoded similarly to |
| | | an L(n). Return value of |
| | | read_signed_literal(d, n). These are |
| | | rare. |
| | | |
| P(8) | | An 8-bit probability. No different from |
| | | an L(8), but we sometimes use this |
| | | notation to emphasize that a probability |
| | | is being coded. |
| | | |
| P(7) | | A 7-bit specification of an 8-bit |
| | | probability. Coded as an L(7) number x; |
| | | the resulting 8-bit probability is x ? x |
| | | << 1 : 1. |
| | | |
| F? X | | A flag that, if true, is followed by a |
| | | piece of data X. |
| | | |
Bankoski, et al. Informational [Page 25]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
| F? X:Y | | A flag that, if true, is followed by X |
| | | and, if false, is followed by Y. Also |
| | | used to express a value where Y is an |
| | | implicit default (not encoded in the data |
| | | stream), as in F? P(8):255, which |
| | | expresses an optional probability: If the |
| | | flag is true, the probability is specified |
| | | as an 8-bit literal, while if the flag is |
| | | false, the probability defaults to 255. |
| | | |
| B(p)? X | B(p)? | Variants of the above using a boolean |
| | X:Y | indicator whose probability is not |
| | | necessarily 128. |
| | | |
| T | | Tree-encoded value from small alphabet. |
+--------------+-------+--------------------------------------------+
The last type requires elaboration. We often wish to encode
something whose value is restricted to a small number of
possibilities (the alphabet).
This is done by representing the alphabet as the leaves of a small
binary tree. The (non-leaf) nodes of the tree have associated
probabilities p and correspond to calls to read_bool(d, p). We think
of a zero as choosing the left branch below the node and a one as
choosing the right branch.
Thus, every value (leaf) whose tree depth is x is decoded after
exactly x calls to read_bool.
A tree representing an encoding of an alphabet of n possible values
always contains n-1 non-leaf nodes, regardless of its shape (this is
easily seen by induction on n).
There are many ways that a given alphabet can be so represented. The
choice of tree has little impact on datarate but does affect decoder
performance. The trees used by VP8 are chosen to (on average)
minimize the number of calls to read_bool. This amounts to shaping
the tree so that values that are more probable have smaller tree
depth than do values that are less probable.
Readers familiar with Huffman coding will notice that, given an
alphabet together with probabilities for each value, the associated
Huffman tree minimizes the expected number of calls to read_bool.
Bankoski, et al. Informational [Page 26]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
Such readers will also realize that the coding method described here
never results in higher datarates than does the Huffman method and,
indeed, often results in much lower datarates. Huffman coding is, in
fact, nothing more than a special case of this method in which each
node probability is fixed at 128 (i.e., 1/2).
8.1. Tree Coding Implementation
We give a suggested implementation of a tree data structure followed
by a couple of actual examples of its usage by VP8.
It is most convenient to represent the values using small positive
integers, typically an enum counting up from zero. The largest
alphabet (used to code DCT coefficients, described in Section 13)
that is tree-coded by VP8 has only 12 values. The tree for this
alphabet adds 11 interior nodes and so has a total of 23 positions.
Thus, an 8-bit number easily accommodates both a tree position and a
return value.
A tree may then be compactly represented as an array of (pairs of)
8-bit integers. Each (even) array index corresponds to an interior
node of the tree; the 0th index of course corresponds to the root of
the tree. The array entries come in pairs corresponding to the left
(0) and right (1) branches of the subtree below the interior node.
We use the convention that a positive (even) branch entry is the
index of a deeper interior node, while a nonpositive entry v
corresponds to a leaf whose value is -v.
The node probabilities associated to a tree-coded value are stored in
an array whose indices are half the indices of the corresponding tree
positions. The length of the probability array is one less than the
size of the alphabet.
Here is C code implementing the foregoing. The advantages of our
data structure should be noted. Aside from the smallness of the
structure itself, the tree-directed reading algorithm is essentially
a single line of code.
Bankoski, et al. Informational [Page 27]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
---- Begin code block --------------------------------------
/* A tree specification is simply an array of 8-bit integers. */
typedef int8 tree_index;
typedef const tree_index Tree[];
/* Read and return a tree-coded value at the current decoder
position. */
int treed_read(
bool_decoder * const d, /* bool_decoder always returns a 0 or 1 */
Tree t, /* tree specification */
const Prob p[] /* corresponding interior node probabilities */
) {
register tree_index i = 0; /* begin at root */
/* Descend tree until leaf is reached */
while ((i = t[ i + read_bool(d, p[i>>1])]) > 0) {}
return -i; /* return value is negation of nonpositive index */
}
---- End code block ----------------------------------------
Tree-based decoding is implemented in the reference decoder file
bool_decoder.h (Section 20.2).
8.2. Tree Coding Example
As a multi-part example, without getting too far into the semantics
of macroblock decoding (which is of course taken up below), we look
at the "mode" coding for intra-predicted macroblocks.
It so happens that, because of a difference in statistics, the Y (or
luma) mode encoding uses two different trees: one for key frames and
another for interframes. This is the only instance in VP8 of the
same dataset being coded by different trees under different
circumstances. The UV (or chroma) modes are a proper subset of the Y
modes and, as such, have their own decoding tree.
Bankoski, et al. Informational [Page 28]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
---- Begin code block --------------------------------------
typedef enum
{
DC_PRED, /* predict DC using row above and column to the left */
V_PRED, /* predict rows using row above */
H_PRED, /* predict columns using column to the left */
TM_PRED, /* propagate second differences a la "True Motion" */
B_PRED, /* each Y subblock is independently predicted */
num_uv_modes = B_PRED, /* first four modes apply to chroma */
num_ymodes /* all modes apply to luma */
}
intra_mbmode;
/* The aforementioned trees together with the implied codings as
comments.
Actual (i.e., positive) indices are always even.
Value (i.e., nonpositive) indices are arbitrary. */
const tree_index ymode_tree [2 * (num_ymodes - 1)] =
{
-DC_PRED, 2, /* root: DC_PRED = "0", "1" subtree */
4, 6, /* "1" subtree has 2 descendant subtrees */
-V_PRED, -H_PRED, /* "10" subtree: V_PRED = "100",
H_PRED = "101" */
-TM_PRED, -B_PRED /* "11" subtree: TM_PRED = "110",
B_PRED = "111" */
};
const tree_index kf_ymode_tree [2 * (num_ymodes - 1)] =
{
-B_PRED, 2, /* root: B_PRED = "0", "1" subtree */
4, 6, /* "1" subtree has 2 descendant subtrees */
-DC_PRED, -V_PRED, /* "10" subtree: DC_PRED = "100",
V_PRED = "101" */
-H_PRED, -TM_PRED /* "11" subtree: H_PRED = "110",
TM_PRED = "111" */
};
Bankoski, et al. Informational [Page 29]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
const tree_index uv_mode_tree [2 * (num_uv_modes - 1)] =
{
-DC_PRED, 2, /* root: DC_PRED = "0", "1" subtree */
-V_PRED, 4, /* "1" subtree: V_PRED = "10",
"11" subtree */
-H_PRED, -TM_PRED /* "11" subtree: H_PRED = "110",
TM_PRED = "111" */
};
/* Given a bool_decoder d, a Y mode might be decoded as follows. */
const Prob pretend_its_huffman [num_ymodes - 1] =
{ 128, 128, 128, 128};
Ymode = (intra_mbmode) treed_read(d, ymode_tree,
pretend_its_huffman);
---- End code block ----------------------------------------
Since it greatly facilitates re-use of reference code, and since
there is no real reason to do otherwise, it is strongly suggested
that any decoder implementation use exactly the same enumeration
values and probability table layouts as those described in this
document (and in the reference code) for all tree-coded data in VP8.
9. Frame Header
The uncompressed data chunk at the start of each frame and at the
first part of the first data partition contains information
pertaining to the frame as a whole. We list the fields in the order
of occurrence. Most of the header decoding occurs in the reference
decoder file dixie.c (Section 20.4).
9.1. Uncompressed Data Chunk
The uncompressed data chunk comprises a common (for key frames and
interframes) 3-byte frame tag that contains four fields, as follows:
1. A 1-bit frame type (0 for key frames, 1 for interframes).
2. A 3-bit version number (0 - 3 are defined as four different
profiles with different decoding complexity; other values may be
defined for future variants of the VP8 data format).
Bankoski, et al. Informational [Page 30]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
3. A 1-bit show_frame flag (0 when current frame is not for display,
1 when current frame is for display).
4. A 19-bit field containing the size of the first data partition in
bytes.
The version number setting enables or disables certain features in
the bitstream, as follows:
+---------+-------------------------+-------------+
| Version | Reconstruction Filter | Loop Filter |
+---------+-------------------------+-------------+
| 0 | Bicubic | Normal |
| | | |
| 1 | Bilinear | Simple |
| | | |
| 2 | Bilinear | None |
| | | |
| 3 | None | None |
| | | |
| Other | Reserved for future use | |
+---------+-------------------------+-------------+
The reference software also adjusts the loop filter based on version
number, as per the table above. Version number 1 implies a "simple"
loop filter, and version numbers 2 and 3 imply no loop filter.
However, the "simple" filter setting in this context has no effect
whatsoever on the decoding process, and the "no loop filter" setting
only forces the reference encoder to set filter level equal to 0.
Neither affect the decoding process. In decoding, the only loop
filter settings that matter are those in the frame header.
For key frames, the frame tag is followed by a further 7 bytes of
uncompressed data, as follows:
---- Begin code block --------------------------------------
Start code byte 0 0x9d
Start code byte 1 0x01
Start code byte 2 0x2a
16 bits : (2 bits Horizontal Scale << 14) | Width (14 bits)
16 bits : (2 bits Vertical Scale << 14) | Height (14 bits)
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 31]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
The following source code segment illustrates validation of the start
code and reading the width, height, and scale factors for a key
frame.
---- Begin code block --------------------------------------
unsigned char *c = pbi->source+3;
// vet via sync code
if (c[0]!=0x9d||c[1]!=0x01||c[2]!=0x2a)
return -1;
---- End code block ----------------------------------------
Where pbi->source points to the beginning of the frame.
The following code reads the image dimension from the bitstream:
---- Begin code block --------------------------------------
pc->Width = swap2(*(unsigned short*)(c+3))&0x3fff;
pc->horiz_scale = swap2(*(unsigned short*)(c+3))>>14;
pc->Height = swap2(*(unsigned short*)(c+5))&0x3fff;
pc->vert_scale = swap2(*(unsigned short*)(c+5))>>14;
---- End code block ----------------------------------------
Where the swap2 macro takes care of the endian on a different
platform:
---- Begin code block --------------------------------------
#if defined(__ppc__) || defined(__ppc64__)
# define swap2(d) \
((d&0x000000ff)<<8) | \
((d&0x0000ff00)>>8)
#else
# define swap2(d) d
#endif
---- End code block ----------------------------------------
While each frame is encoded as a raster scan of 16x16 macroblocks,
the frame dimensions are not necessarily evenly divisible by 16. In
this case, write ew = 16 - (width & 15) and eh = 16 - (height & 15)
for the excess width and height, respectively. Although they are
Bankoski, et al. Informational [Page 32]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
encoded, the last ew columns and eh rows are not actually part of the
image and should be discarded before final output. However, these
"excess pixels" should be maintained in the internal reconstruction
buffer used to predict ensuing frames.
The scaling specifications for each dimension are encoded as follows.
+-------+--------------------------------------+
| Value | Scaling |
+-------+--------------------------------------+
| 0 | No upscaling (the most common case). |
| | |
| 1 | Upscale by 5/4. |
| | |
| 2 | Upscale by 5/3. |
| | |
| 3 | Upscale by 2. |
+-------+--------------------------------------+
Upscaling does not affect the reconstruction buffer, which should be
maintained at the encoded resolution. Any reasonable method of
upsampling (including any that may be supported by video hardware in
the playback environment) may be used. Since scaling has no effect
on decoding, we do not discuss it any further.
As discussed in Section 5, allocation (or re-allocation) of data
structures (such as the reconstruction buffer) whose size depends on
dimension will be triggered here.
9.2. Color Space and Pixel Type (Key Frames Only)
+-------+------------------------------------------+
| Field | Value |
+-------+------------------------------------------+
| L(1) | 1-bit color space type specification |
| | |
| L(1) | 1-bit pixel value clamping specification |
+-------+------------------------------------------+
The color space type bit is encoded as follows:
o 0 - YUV color space similar to the YCrCb color space defined in
[ITU-R_BT.601]
o 1 - Reserved for future use
Bankoski, et al. Informational [Page 33]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
The pixel value clamping type bit is encoded as follows:
o 0 - Decoders are required to clamp the reconstructed pixel values
to between 0 and 255 (inclusive).
o 1 - Reconstructed pixel values are guaranteed to be between 0 and
255; no clamping is necessary.
Information in this subsection does not appear in interframes.
9.3. Segment-Based Adjustments
This subsection contains probability and value information for
implementing segment adaptive adjustments to default decoder
behavior. The data in this subsection is used in the decoding of the
ensuing per-segment information and applies to the entire frame.
When segment adaptive adjustments are enabled, each macroblock will
be assigned a segment ID. Macroblocks with the same segment ID
belong to the same segment and have the same adaptive adjustments
over default baseline values for the frame. The adjustments can be
quantizer level or loop filter strength.
The context for decoding this feature at the macroblock level is
provided by a subsection in the frame header, which contains:
1. A segmentation_enabled flag that enables the feature for this
frame if set to 1, and disables it if set to 0. The following
fields occur if the feature is enabled.
2. L(1) indicates if the segment map is updated for the current
frame (update_mb_segmentation_map).
3. L(1) indicates if the segment feature data items are updated for
the current frame (update_segment_feature_data).
4. If Item 3 above (update_segment_feature_data) is 1, the following
fields occur:
a. L(1), the mode of segment feature data
(segment_feature_mode), can be absolute-value mode (0) or
delta value mode (1).
Bankoski, et al. Informational [Page 34]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
b. Segment feature data items are decoded segment by segment for
each segment feature. For every data item, a one-bit flag
indicates whether the item is 0, or a non-zero value to be
decoded. If the value is non-zero, then the value is decoded
as a magnitude L(n), followed by a one-bit sign (L(1) -- 0
for positive and 1 for negative). The length n can be looked
up from a pre-defined length table for all feature data.
5. If the L(1) flag as noted in Item 2 above is set to 1, the
probabilities of the decoding tree for the segment map are
decoded from the bitstream. Each probability is decoded with a
one-bit flag indicating whether the probability is the default
value of 255 (flag is set to 0), or an 8-bit value, L(8), from
the bitstream.
The layout and semantics supporting this feature at the macroblock
level are described in Section 10.
9.4. Loop Filter Type and Levels
VP8 supports two types of loop filters having different computational
complexity. The following bits occur in the header to support the
selection of the baseline type, strength, and sharpness behavior of
the loop filter used for the current frame.
+-------+-------------------+
| Index | Description |
+-------+-------------------+
| L(1) | filter_type |
| | |
| L(6) | loop_filter_level |
| | |
| L(3) | sharpness_level |
+-------+-------------------+
The meaning of these numbers will be further explained in Section 15.
VP8 has a feature in the bitstream that enables adjustment of the
loop filter level based on a macroblock's prediction mode and
reference frame. The per-macroblock adjustment is done through delta
values against the default loop filter level for the current frame.
This subsection contains flag and value information for implementing
per-macroblock loop filter level adjustment to default decoder
behavior. The data in this section is used in the decoding of the
ensuing per-macroblock information and applies to the entire frame.
Bankoski, et al. Informational [Page 35]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
L(1) is a one-bit flag indicating if the macroblock loop filter
adjustment is on for the current frame. 0 means that such a feature
is not supported in the current frame, and 1 means this feature is
enabled for the current frame.
Whether the adjustment is based on a reference frame or encoding
mode, the adjustment of the loop filter level is done via a delta
value against a baseline loop filter value. The delta values are
updated for the current frame if an L(1) bit,
mode_ref_lf_delta_update, takes the value 1. There are two groups of
delta values: One group of delta values is for reference frame-based
adjustments, and the other group is for mode-based adjustments. The
number of delta values in the two groups is MAX_REF_LF_DELTAS and
MAX_MODE_LF_DELTAS, respectively. For every value within the two
groups, there is a one-bit L(1) to indicate if the particular value
is updated. When one is updated (1), it is transmitted as a six-bit-
magnitude L(6) followed by a one-bit sign flag (L(1) -- 0 for
positive and 1 for negative).
9.5. Token Partition and Partition Data Offsets
VP8 allows DCT coefficients to be packed into multiple partitions,
besides the first partition with header and per-macroblock prediction
information, so the decoder can perform parallel decoding in an
efficient manner. A two-bit L(2) is used to indicate the number of
coefficient data partitions within a compressed frame. The two bits
are defined in the following table:
+-------+-------+----------------------+
| Bit 1 | Bit 0 | Number of Partitions |
+-------+-------+----------------------+
| 0 | 0 | 1 |
| | | |
| 0 | 1 | 2 |
| | | |
| 1 | 0 | 4 |
| | | |
| 1 | 1 | 8 |
+-------+-------+----------------------+
Offsets are embedded in the bitstream to provide the decoder direct
access to token partitions. If the number of data partitions is
greater than 1, the size of each partition (except the last) is
written in 3 bytes (24 bits). The size of the last partition is the
remainder of the data not used by any of the previous partitions.
Bankoski, et al. Informational [Page 36]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
The partitioned data are consecutive in the bitstream, so the size
can also be used to calculate the offset of each partition. The
following pseudocode illustrates how the size/offset is defined by
the three bytes in the bitstream.
---- Begin code block --------------------------------------
Offset/size = (uint32)(byte0) + ((uint32)(byte1)<<8)
+ ((uint32)(byte2)<<16);
---- End code block ----------------------------------------
9.6. Dequantization Indices
All residue signals are specified via a quantized 4x4 DCT applied to
the Y, U, V, or Y2 subblocks of a macroblock. As detailed in
Section 14, before inverting the transform, each decoded coefficient
is multiplied by one of six dequantization factors, the choice of
which depends on the plane (Y, chroma = U or V, Y2) and coefficient
position (DC = coefficient 0, AC = coefficients 1-15). The six
values are specified using 7-bit indices into six corresponding fixed
tables (the tables are given in Section 14).
The first 7-bit index gives the dequantization table index for
Y-plane AC coefficients, called yac_qi. It is always coded and acts
as a baseline for the other 5 quantization indices, each of which is
represented by a delta from this baseline index. Pseudocode for
reading the indices follows:
---- Begin code block --------------------------------------
yac_qi = L(7); /* Y ac index always specified */
ydc_delta = F? delta(): 0; /* Y dc delta specified if
flag is true */
y2dc_delta = F? delta(): 0; /* Y2 dc delta specified if
flag is true */
y2ac_delta = F? delta(): 0; /* Y2 ac delta specified if
flag is true */
uvdc_delta = F? delta(): 0; /* chroma dc delta specified
if flag is true */
uvac_delta = F? delta(): 0; /* chroma ac delta specified
if flag is true */
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 37]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
Where delta() is the process to read 5 bits from the bitstream to
determine a signed delta value:
+-------+--------------------------------------------------+
| Index | Description |
+-------+--------------------------------------------------+
| L(4) | Magnitude of delta |
| | |
| L(1) | Sign of delta, 0 for positive and 1 for negative |
+-------+--------------------------------------------------+
9.7. Refresh Golden Frame and Altref Frame
For key frames, both the golden frame and the altref frame are
refreshed/ replaced by the current reconstructed frame, by default.
For non-key frames, VP8 uses two bits to indicate whether the two
frame buffers are refreshed, using the reconstructed current frame:
+-------+----------------------------------------------------------+
| Index | Description |
+-------+----------------------------------------------------------+
| L(1) | Whether golden frame is refreshed (0 for no, 1 for yes). |
| | |
| L(1) | Whether altref frame is refreshed (0 for no, 1 for yes). |
+-------+----------------------------------------------------------+
When the flag for the golden frame is 0, VP8 uses 2 more bits in the
bitstream to indicate whether the buffer (and which buffer) is copied
to the golden frame, or if no buffer is copied:
+-------+------------------------------------------+
| Index | Description |
+-------+------------------------------------------+
| L(2) | Buffer copy flag for golden frame buffer |
+-------+------------------------------------------+
Where:
o 0 means no buffer is copied to the golden frame
o 1 means last_frame is copied to the golden frame
o 2 means alt_ref_frame is copied to the golden frame
Similarly, when the flag for altref is 0, VP8 uses 2 bits in the
bitstream to indicate which buffer is copied to alt_ref_frame.
Bankoski, et al. Informational [Page 38]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
+-------+------------------------------------------+
| Index | Description |
+-------+------------------------------------------+
| L(2) | Buffer copy flag for altref frame buffer |
+-------+------------------------------------------+
Where:
o 0 means no buffer is copied to the altref frame
o 1 means last_frame is copied to the altref frame
o 2 means golden_frame is copied to the altref frame
Two bits are transmitted for ref_frame_sign_bias for golden_frame and
alt_ref_frame, respectively.
+-------+---------------------------------+
| Index | Description |
+-------+---------------------------------+
| L(1) | Sign bias flag for golden frame |
| | |
| L(1) | Sign bias flag for altref frame |
+-------+---------------------------------+
These values are used to control the sign of the motion vectors when
a golden frame or an altref frame is used as the reference frame for
a macroblock.
9.8. Refresh Last Frame Buffer
VP8 uses one bit, L(1), to indicate if the last frame reference
buffer is refreshed using the constructed current frame. On a key
frame, this bit is overridden, and the last frame buffer is always
refreshed.
9.9. DCT Coefficient Probability Update
This field contains updates to the probability tables used to decode
DCT coefficients. For each of the probabilities in the tables, there
is an L(1) flag indicating if the probability is updated for the
current frame, and if the L(1) flag is set to 1, there follows an
additional 8-bit value representing the new probability value. These
tables are maintained across interframes but are of course replaced
with their defaults at the beginning of every key frame.
The layout and semantics of this field will be taken up in
Section 13.
Bankoski, et al. Informational [Page 39]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
9.10. Remaining Frame Header Data (Non-Key Frame)
+-------+-----------------------------------------------------------+
| Index | Description |
+-------+-----------------------------------------------------------+
| L(1) | mb_no_skip_coeff. This flag indicates at the frame level |
| | if skipping of macroblocks with no non-zero coefficients |
| | is enabled. If it is set to 0, then prob_skip_false is |
| | not read and mb_skip_coeff is forced to 0 for all |
| | macroblocks (see Sections 11.1 and 12.1). |
| | |
| L(8) | prob_skip_false = probability used for decoding a |
| | macroblock-level flag, which indicates if a macroblock |
| | has any non-zero coefficients. Only read if |
| | mb_no_skip_coeff is 1. |
| | |
| L(8) | prob_intra = probability that a macroblock is "intra" |
| | predicted (that is, predicted from the already-encoded |
| | portions of the current frame), as opposed to "inter" |
| | predicted (that is, predicted from the contents of a |
| | prior frame). |
| | |
| L(8) | prob_last = probability that an inter-predicted |
| | macroblock is predicted from the immediately previous |
| | frame, as opposed to the most recent golden frame or |
| | altref frame. |
| | |
| L(8) | prob_gf = probability that an inter-predicted macroblock |
| | is predicted from the most recent golden frame, as |
| | opposed to the altref frame. |
| | |
| F | If true, followed by four L(8)s updating the |
| | probabilities for the different types of intra-prediction |
| | for the Y plane. These probabilities correspond to the |
| | four interior nodes of the decoding tree for intra-Y |
| | modes in an interframe, that is, the even positions in |
| | the ymode_tree array given above. |
| | |
| F | If true, followed by three L(8)s updating the |
| | probabilities for the different types of intra-prediction |
| | for the chroma planes. These probabilities correspond to |
| | the even positions in the uv_mode_tree array given above. |
| | |
| X | Motion vector probability update. Details are given in |
| | Section 17.2, "Probability Updates". |
+-------+-----------------------------------------------------------+
Bankoski, et al. Informational [Page 40]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
Decoding of this portion of the frame header is handled in the
reference decoder file dixie.c (Section 20.4).
9.11. Remaining Frame Header Data (Key Frame)
+-------+-----------------------------------------------------------+
| Index | Description |
+-------+-----------------------------------------------------------+
| L(1) | mb_no_skip_coeff. This flag indicates at the frame level |
| | if skipping of macroblocks with no non-zero coefficients |
| | is enabled. If it is set to 0, then prob_skip_false is |
| | not read and mb_skip_coeff is forced to 0 for all |
| | macroblocks (see Sections 11.1 and 12.1). |
| | |
| L(8) | prob_skip_false = Probability used for decoding a |
| | macroblock-level flag, which indicates if a macroblock |
| | has any non-zero coefficients. Only read if |
| | mb_no_skip_coeff is 1. |
+-------+-----------------------------------------------------------+
Decoding of this portion of the frame header is handled in the
reference decoder file modemv.c (Section 20.11).
This completes the layout of the frame header. The remainder of the
first data partition consists of macroblock-level prediction data.
After the frame header is processed, all probabilities needed to
decode the prediction and residue data are known and will not change
until the next frame.
10. Segment-Based Feature Adjustments
Every macroblock may optionally override some of the default
behaviors of the decoder. Specifically, VP8 uses segment-based
adjustments to support changing quantizer level and loop filter level
for a macroblock. When the segment-based adjustment feature is
enabled for a frame, each macroblock within the frame is coded with a
segment_id. This effectively segments all the macroblocks in the
current frame into a number of different segments. Macroblocks
within the same segment behave exactly the same for quantizer and
loop filter level adjustments.
If both the segmentation_enabled and update_mb_segmentation_map flags
in subsection B of the frame header take a value of 1, the prediction
data for each (intra- or inter-coded) macroblock begins with a
specification of segment_id for the current macroblock. It is
decoded using this simple tree ...
Bankoski, et al. Informational [Page 41]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
---- Begin code block --------------------------------------
const tree_index mb_segment_tree [2 * (4-1)] =
{
2, 4, /* root: "0", "1" subtrees */
-0, -1, /* "00" = 0th value, "01" = 1st value */
-2, -3 /* "10" = 2nd value, "11" = 3rd value */
}
---- End code block ----------------------------------------
... combined with a 3-entry probability table,
mb_segment_tree_probs[3]. The macroblock's segment_id is used later
in the decoding process to look into the segment_feature_data table
and determine how the quantizer and loop filter levels are adjusted.
The decoding of segment_id, together with the parsing of
intra-prediction modes (which is taken up next), is implemented in
the reference decoder file modemv.c.
11. Key Frame Macroblock Prediction Records
After specifying the features described above, the macroblock
prediction record next specifies the prediction mode used for the
macroblock.
11.1. mb_skip_coeff
The single bool flag is decoded using prob_skip_false if and only if
mb_no_skip_coeff is set to 1 (see Sections 9.10 and 9.11). If
mb_no_skip_coeff is set to 0, then this value defaults to 0.
11.2. Luma Modes
First comes the luma specification of type intra_mbmode, coded using
the kf_ymode_tree, as described in Section 8 and repeated here for
convenience:
Bankoski, et al. Informational [Page 42]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
---- Begin code block --------------------------------------
typedef enum
{
DC_PRED, /* predict DC using row above and column to the left */
V_PRED, /* predict rows using row above */
H_PRED, /* predict columns using column to the left */
TM_PRED, /* propagate second differences a la "True Motion" */
B_PRED, /* each Y subblock is independently predicted */
num_uv_modes = B_PRED, /* first four modes apply to chroma */
num_ymodes /* all modes apply to luma */
}
intra_mbmode;
const tree_index kf_ymode_tree [2 * (num_ymodes - 1)] =
{
-B_PRED, 2, /* root: B_PRED = "0", "1" subtree */
4, 6, /* "1" subtree has 2 descendant subtrees */
-DC_PRED, -V_PRED, /* "10" subtree: DC_PRED = "100",
V_PRED = "101" */
-H_PRED, -TM_PRED /* "11" subtree: H_PRED = "110",
TM_PRED = "111" */
};
---- End code block ----------------------------------------
For key frames, the Y mode is decoded using a fixed probability array
as follows:
---- Begin code block --------------------------------------
const Prob kf_ymode_prob [num_ymodes - 1] = { 145, 156, 163, 128};
Ymode = (intra_mbmode) treed_read(d, kf_ymode_tree, kf_ymode_prob);
---- End code block ----------------------------------------
d is of course the bool_decoder being used to read the first data
partition.
If the Ymode is B_PRED, it is followed by a (tree-coded) mode for
each of the 16 Y subblocks. The 10 subblock modes and their coding
tree are as follows:
Bankoski, et al. Informational [Page 43]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
---- Begin code block --------------------------------------
typedef enum
{
B_DC_PRED, /* predict DC using row above and column
to the left */
B_TM_PRED, /* propagate second differences a la
"True Motion" */
B_VE_PRED, /* predict rows using row above */
B_HE_PRED, /* predict columns using column to the left */
B_LD_PRED, /* southwest (left and down) 45 degree diagonal
prediction */
B_RD_PRED, /* southeast (right and down) "" */
B_VR_PRED, /* SSE (vertical right) diagonal prediction */
B_VL_PRED, /* SSW (vertical left) "" */
B_HD_PRED, /* ESE (horizontal down) "" */
B_HU_PRED, /* ENE (horizontal up) "" */
num_intra_bmodes
}
intra_bmode;
/* Coding tree for the above, with implied codings as comments */
const tree_index bmode_tree [2 * (num_intra_bmodes - 1)] =
{
-B_DC_PRED, 2, /* B_DC_PRED = "0" */
-B_TM_PRED, 4, /* B_TM_PRED = "10" */
-B_VE_PRED, 6, /* B_VE_PRED = "110" */
8, 12,
-B_HE_PRED, 10, /* B_HE_PRED = "11100" */
-B_RD_PRED, -B_VR_PRED, /* B_RD_PRED = "111010",
B_VR_PRED = "111011" */
-B_LD_PRED, 14, /* B_LD_PRED = "111110" */
-B_VL_PRED, 16, /* B_VL_PRED = "1111110" */
-B_HD_PRED, -B_HU_PRED /* HD = "11111110",
HU = "11111111" */
};
---- End code block ----------------------------------------
The first four modes are smaller versions of the similarly named
16x16 modes above, albeit with slightly different numbering. The
last six "diagonal" modes are unique to luma subblocks.
Bankoski, et al. Informational [Page 44]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
11.3. Subblock Mode Contexts
The coding of subblock modes in key frames uses the modes already
coded for the subblocks to the left of and above the subblock to
select a probability array for decoding the current subblock mode.
This is our first instance of contextual prediction, and there are
several caveats associated with it:
1. The adjacency relationships between subblocks are based on the
normal default raster placement of the subblocks.
2. The adjacent subblocks need not lie in the current macroblock.
The subblocks to the left of the left-edge subblocks 0, 4, 8, and
12 are the right-edge subblocks 3, 7, 11, and 15, respectively,
of the (already coded) macroblock immediately to the left.
Similarly, the subblocks above the top-edge subblocks 0, 1, 2,
and 3 are the bottom-edge subblocks 12, 13, 14, and 15 of the
already-coded macroblock immediately above us.
3. For macroblocks on the top row or left edge of the image, some of
the predictors will be non-existent. Such predictors are taken
to have had the value B_DC_PRED, which, perhaps conveniently,
takes the value 0 in the enumeration above. A simple management
scheme for these contexts might maintain a row of above
predictors and four left predictors. Before decoding the frame,
the entire row is initialized to B_DC_PRED; before decoding each
row of macroblocks, the four left predictors are also set to
B_DC_PRED. After decoding a macroblock, the bottom four subblock
modes are copied into the row predictor (at the current position,
which then advances to be above the next macroblock), and the
right four subblock modes are copied into the left predictor.
4. Many macroblocks will of course be coded using a 16x16 luma
prediction mode. For the purpose of predicting ensuing subblock
modes (only), such macroblocks derive a subblock mode, constant
throughout the macroblock, from the 16x16 luma mode as follows:
DC_PRED uses B_DC_PRED, V_PRED uses B_VE_PRED, H_PRED uses
B_HE_PRED, and TM_PRED uses B_TM_PRED.
5. Although we discuss interframe modes in Section 16, we remark
here that, while interframes do use all the intra-coding modes
described here and below, the subblock modes in an interframe are
coded using a single constant probability array that does not
depend on any context.
The dependence of subblock mode probability on the nearby subblock
mode context is most easily handled using a three-dimensional
constant array:
Bankoski, et al. Informational [Page 45]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
---- Begin code block --------------------------------------
const Prob kf_bmode_prob [num_intra_bmodes] [num_intra_bmodes]
[num_intra_bmodes-1];
---- End code block ----------------------------------------
The outer two dimensions of this array are indexed by the already-
coded subblock modes above and to the left of the current block,
respectively. The inner dimension is a typical tree probability list
whose indices correspond to the even indices of the bmode_tree above.
The mode for the j^(th) luma subblock is then
---- Begin code block --------------------------------------
Bmode = (intra_bmode) treed_read(d, bmode_tree, kf_bmode_prob
[A] [L]);
---- End code block ----------------------------------------
Where the 4x4 Y subblock index j varies from 0 to 15 in raster order,
and A and L are the modes used above and to the left of the j^(th)
subblock.
The contents of the kf_bmode_prob array are given at the end of this
section.
11.4. Chroma Modes
After the Y mode (and optional subblock mode) specification comes the
chroma mode. The chroma modes are a subset of the Y modes and are
coded using the uv_mode_tree, as described in Section 8 and repeated
here for convenience:
---- Begin code block --------------------------------------
const tree_index uv_mode_tree [2 * (num_uv_modes - 1)] =
{
-DC_PRED, 2, /* root: DC_PRED = "0", "1" subtree */
-V_PRED, 4, /* "1" subtree: V_PRED = "10",
"11" subtree */
-H_PRED, -TM_PRED /* "11" subtree: H_PRED = "110",
TM_PRED = "111" */
};
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 46]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
As for the Y modes (in a key frame), the chroma modes are coded using
a fixed, contextless probability table:
---- Begin code block --------------------------------------
const Prob kf_uv_mode_prob [num_uv_modes - 1] = { 142, 114, 183};
uv_mode = (intra_mbmode) treed_read(d, uv_mode_tree,
kf_uv_mode_prob);
---- End code block ----------------------------------------
This completes the description of macroblock prediction coding for
key frames. As will be discussed in Section 16, the coding of intra
modes within interframes is similar, but not identical, to that
described here (and in the reference code) for prediction modes and,
indeed, for all tree-coded data in VP8.
11.5. Subblock Mode Probability Table
Finally, here is the fixed probability table used to decode subblock
modes in key frames.
---- Begin code block --------------------------------------
const Prob kf_bmode_prob [num_intra_bmodes] [num_intra_bmodes]
[num_intra_bmodes-1] =
{
{
{ 231, 120, 48, 89, 115, 113, 120, 152, 112},
{ 152, 179, 64, 126, 170, 118, 46, 70, 95},
{ 175, 69, 143, 80, 85, 82, 72, 155, 103},
{ 56, 58, 10, 171, 218, 189, 17, 13, 152},
{ 144, 71, 10, 38, 171, 213, 144, 34, 26},
{ 114, 26, 17, 163, 44, 195, 21, 10, 173},
{ 121, 24, 80, 195, 26, 62, 44, 64, 85},
{ 170, 46, 55, 19, 136, 160, 33, 206, 71},
{ 63, 20, 8, 114, 114, 208, 12, 9, 226},
{ 81, 40, 11, 96, 182, 84, 29, 16, 36}
},
Bankoski, et al. Informational [Page 47]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{
{ 134, 183, 89, 137, 98, 101, 106, 165, 148},
{ 72, 187, 100, 130, 157, 111, 32, 75, 80},
{ 66, 102, 167, 99, 74, 62, 40, 234, 128},
{ 41, 53, 9, 178, 241, 141, 26, 8, 107},
{ 104, 79, 12, 27, 217, 255, 87, 17, 7},
{ 74, 43, 26, 146, 73, 166, 49, 23, 157},
{ 65, 38, 105, 160, 51, 52, 31, 115, 128},
{ 87, 68, 71, 44, 114, 51, 15, 186, 23},
{ 47, 41, 14, 110, 182, 183, 21, 17, 194},
{ 66, 45, 25, 102, 197, 189, 23, 18, 22}
},
{
{ 88, 88, 147, 150, 42, 46, 45, 196, 205},
{ 43, 97, 183, 117, 85, 38, 35, 179, 61},
{ 39, 53, 200, 87, 26, 21, 43, 232, 171},
{ 56, 34, 51, 104, 114, 102, 29, 93, 77},
{ 107, 54, 32, 26, 51, 1, 81, 43, 31},
{ 39, 28, 85, 171, 58, 165, 90, 98, 64},
{ 34, 22, 116, 206, 23, 34, 43, 166, 73},
{ 68, 25, 106, 22, 64, 171, 36, 225, 114},
{ 34, 19, 21, 102, 132, 188, 16, 76, 124},
{ 62, 18, 78, 95, 85, 57, 50, 48, 51}
},
{
{ 193, 101, 35, 159, 215, 111, 89, 46, 111},
{ 60, 148, 31, 172, 219, 228, 21, 18, 111},
{ 112, 113, 77, 85, 179, 255, 38, 120, 114},
{ 40, 42, 1, 196, 245, 209, 10, 25, 109},
{ 100, 80, 8, 43, 154, 1, 51, 26, 71},
{ 88, 43, 29, 140, 166, 213, 37, 43, 154},
{ 61, 63, 30, 155, 67, 45, 68, 1, 209},
{ 142, 78, 78, 16, 255, 128, 34, 197, 171},
{ 41, 40, 5, 102, 211, 183, 4, 1, 221},
{ 51, 50, 17, 168, 209, 192, 23, 25, 82}
},
{
{ 125, 98, 42, 88, 104, 85, 117, 175, 82},
{ 95, 84, 53, 89, 128, 100, 113, 101, 45},
{ 75, 79, 123, 47, 51, 128, 81, 171, 1},
{ 57, 17, 5, 71, 102, 57, 53, 41, 49},
{ 115, 21, 2, 10, 102, 255, 166, 23, 6},
{ 38, 33, 13, 121, 57, 73, 26, 1, 85},
{ 41, 10, 67, 138, 77, 110, 90, 47, 114},
{ 101, 29, 16, 10, 85, 128, 101, 196, 26},
{ 57, 18, 10, 102, 102, 213, 34, 20, 43},
{ 117, 20, 15, 36, 163, 128, 68, 1, 26}
},
Bankoski, et al. Informational [Page 48]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{
{ 138, 31, 36, 171, 27, 166, 38, 44, 229},
{ 67, 87, 58, 169, 82, 115, 26, 59, 179},
{ 63, 59, 90, 180, 59, 166, 93, 73, 154},
{ 40, 40, 21, 116, 143, 209, 34, 39, 175},
{ 57, 46, 22, 24, 128, 1, 54, 17, 37},
{ 47, 15, 16, 183, 34, 223, 49, 45, 183},
{ 46, 17, 33, 183, 6, 98, 15, 32, 183},
{ 65, 32, 73, 115, 28, 128, 23, 128, 205},
{ 40, 3, 9, 115, 51, 192, 18, 6, 223},
{ 87, 37, 9, 115, 59, 77, 64, 21, 47}
},
{
{ 104, 55, 44, 218, 9, 54, 53, 130, 226},
{ 64, 90, 70, 205, 40, 41, 23, 26, 57},
{ 54, 57, 112, 184, 5, 41, 38, 166, 213},
{ 30, 34, 26, 133, 152, 116, 10, 32, 134},
{ 75, 32, 12, 51, 192, 255, 160, 43, 51},
{ 39, 19, 53, 221, 26, 114, 32, 73, 255},
{ 31, 9, 65, 234, 2, 15, 1, 118, 73},
{ 88, 31, 35, 67, 102, 85, 55, 186, 85},
{ 56, 21, 23, 111, 59, 205, 45, 37, 192},
{ 55, 38, 70, 124, 73, 102, 1, 34, 98}
},
{
{ 102, 61, 71, 37, 34, 53, 31, 243, 192},
{ 69, 60, 71, 38, 73, 119, 28, 222, 37},
{ 68, 45, 128, 34, 1, 47, 11, 245, 171},
{ 62, 17, 19, 70, 146, 85, 55, 62, 70},
{ 75, 15, 9, 9, 64, 255, 184, 119, 16},
{ 37, 43, 37, 154, 100, 163, 85, 160, 1},
{ 63, 9, 92, 136, 28, 64, 32, 201, 85},
{ 86, 6, 28, 5, 64, 255, 25, 248, 1},
{ 56, 8, 17, 132, 137, 255, 55, 116, 128},
{ 58, 15, 20, 82, 135, 57, 26, 121, 40}
},
{
{ 164, 50, 31, 137, 154, 133, 25, 35, 218},
{ 51, 103, 44, 131, 131, 123, 31, 6, 158},
{ 86, 40, 64, 135, 148, 224, 45, 183, 128},
{ 22, 26, 17, 131, 240, 154, 14, 1, 209},
{ 83, 12, 13, 54, 192, 255, 68, 47, 28},
{ 45, 16, 21, 91, 64, 222, 7, 1, 197},
{ 56, 21, 39, 155, 60, 138, 23, 102, 213},
{ 85, 26, 85, 85, 128, 128, 32, 146, 171},
{ 18, 11, 7, 63, 144, 171, 4, 4, 246},
{ 35, 27, 10, 146, 174, 171, 12, 26, 128}
},
Bankoski, et al. Informational [Page 49]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{
{ 190, 80, 35, 99, 180, 80, 126, 54, 45},
{ 85, 126, 47, 87, 176, 51, 41, 20, 32},
{ 101, 75, 128, 139, 118, 146, 116, 128, 85},
{ 56, 41, 15, 176, 236, 85, 37, 9, 62},
{ 146, 36, 19, 30, 171, 255, 97, 27, 20},
{ 71, 30, 17, 119, 118, 255, 17, 18, 138},
{ 101, 38, 60, 138, 55, 70, 43, 26, 142},
{ 138, 45, 61, 62, 219, 1, 81, 188, 64},
{ 32, 41, 20, 117, 151, 142, 20, 21, 163},
{ 112, 19, 12, 61, 195, 128, 48, 4, 24}
}
};
---- End code block ----------------------------------------
12. Intraframe Prediction
Intraframe prediction uses already-coded macroblocks within the
current frame to approximate the contents of the current macroblock.
It applies to intra-coded macroblocks in an interframe and to all
macroblocks in a key frame.
Relative to the current macroblock "M", the already-coded macroblocks
include all macroblocks above M together with the macroblocks on the
same row as, and to the left of, M, though at most four of these
macroblocks are actually used: the block "A" directly above M, the
blocks immediately to the left and right of A, and the block
immediately to the left of M.
Each of the prediction modes (i.e., means of extrapolation from
already-calculated values) uses fairly simple arithmetic on pixel
values whose positions, relative to the current position, are defined
by the mode.
The chroma (U and V) and luma (Y) predictions are independent of each
other.
The relative addressing of pixels applied to macroblocks on the upper
row or left column of the frame will sometimes cause pixels outside
the visible frame to be referenced. Usually such out-of-bounds
pixels have an assumed value of 129 for pixels to the left of the
leftmost column of the visible frame and 127 for pixels above the top
row of the visible frame (including the special case of the pixel
above and to the left of the top-left pixel in the visible frame).
Exceptions to this (associated to certain modes) will be noted below.
Bankoski, et al. Informational [Page 50]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
The already-coded macroblocks referenced by intra-prediction have
been "reconstructed", that is, have been predicted and residue-
adjusted (as described in Section 14), but have not been loop-
filtered. While it does process the edges between individual
macroblocks and individual subblocks, loop filtering (described in
Section 15) is applied to the frame as a whole, after all of the
macroblocks have been reconstructed.
12.1. mb_skip_coeff
The single bool flag is decoded using prob_skip_false if and only if
mb_no_skip_coeff is set to 1 (see Sections 9.10 and 9.11). If
mb_no_skip_coeff is set to 0, then this value defaults to 0.
12.2. Chroma Prediction
The chroma prediction is a little simpler than the luma prediction,
so we treat it first. Each of the chroma modes treats U and V
identically; that is, the U and V prediction values are calculated in
parallel, using the same relative addressing and arithmetic in each
of the two planes.
The modes extrapolate prediction values using the 8-pixel row "A"
lying immediately above the block (that is, the bottom chroma row of
the macroblock immediately above the current macroblock) and the
8-pixel column "L" immediately to the left of the block (that is, the
rightmost chroma column of the macroblock immediately to the left of
the current macroblock).
Vertical prediction (chroma mode V_PRED) simply fills each 8-pixel
row of the 8x8 chroma block with a copy of the "above" row (A). If
the current macroblock lies on the top row of the frame, all 8 of the
pixel values in A are assigned the value 127.
Similarly, horizontal prediction (H_PRED) fills each 8-pixel column
of the 8x8 chroma block with a copy of the "left" column (L). If the
current macroblock is in the left column of the frame, all 8 pixel
values in L are assigned the value 129.
DC prediction (DC_PRED) fills the 8x8 chroma block with a single
value. In the generic case of a macroblock lying below the top row
and right of the leftmost column of the frame, this value is the
average of the 16 (genuinely visible) pixels in the (union of the)
above row A and left column L.
Otherwise, if the current macroblock lies on the top row of the
frame, the average of the 8 pixels in L is used; if it lies in the
left column of the frame, the average of the 8 pixels in A is used.
Bankoski, et al. Informational [Page 51]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
Note that the averages used in these exceptional cases are not the
same as those that would be arrived at by using the out-of-bounds A
and L values defined for V_PRED and H_PRED. In the case of the
leftmost macroblock on the top row of the frame, the 8x8 block is
simply filled with the constant value 128.
For DC_PRED, apart from the exceptional case of the top-left
macroblock, we are averaging either 16 or 8 pixel values to get a
single prediction value that fills the 8x8 block. The rounding is
done as follows:
---- Begin code block --------------------------------------
int sum; /* sum of 8 or 16 pixels at (at least) 16-bit precision */
int shf; /* base 2 logarithm of the number of pixels (3 or 4) */
Pixel DCvalue = (sum + (1 << (shf-1))) >> shf;
---- End code block ----------------------------------------
Because the summands are all valid pixels, no "clamp" is necessary in
the calculation of DCvalue.
The remaining "True Motion" (TM_PRED) chroma mode gets its name from
an older technique of video compression used by On2 Technologies, to
which it bears some relation. In addition to the row "A" and column
"L", TM_PRED uses the pixel "P" above and to the left of the chroma
block.
Bankoski, et al. Informational [Page 52]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
The following figure gives an example of how TM_PRED works:
---- Begin code block --------------------------------------
|-----|-----|-----|-----|-----|-----|-----|-----|-----|
| P | A0 | A1 | A2 | A3 | A4 | A5 | A6 | A7 |
|-----|-----|-----|-----|-----|-----|-----|-----|-----|
| L0 | X00 | X01 | X02 | X03 | X04 | X05 | X06 | X07 |
|-----|-----|-----|-----|-----|-----|-----|-----|-----|
| L1 | X10 | X11 | X12 | X13 | X14 | X15 | X16 | X17 |
|-----|-----|-----|-----|-----|-----|-----|-----|-----|
| L2 | X20 | X21 | X22 | X23 | X24 | X25 | X26 | X27 |
|-----|-----|-----|-----|-----|-----|-----|-----|-----|
| L3 | X30 | X31 | X32 | X33 | X34 | X35 | X36 | X37 |
|-----|-----|-----|-----|-----|-----|-----|-----|-----|
| L4 | X40 | X41 | X42 | X43 | X44 | X45 | X46 | X47 |
|-----|-----|-----|-----|-----|-----|-----|-----|-----|
| L5 | X50 | X51 | X52 | X53 | X54 | X55 | X56 | X57 |
|-----|-----|-----|-----|-----|-----|-----|-----|-----|
| L6 | X60 | X61 | X62 | X63 | X64 | X65 | X66 | X67 |
|-----|-----|-----|-----|-----|-----|-----|-----|-----|
| L7 | X70 | X71 | X72 | X73 | X74 | X75 | X76 | X77 |
|-----|-----|-----|-----|-----|-----|-----|-----|-----|
---- End code block ----------------------------------------
Where P, As, and Ls represent reconstructed pixel values from
previously coded blocks, and X00 through X77 represent predicted
values for the current block. TM_PRED uses the following equation to
calculate X_ij:
X_ij = L_i + A_j - P (i, j=0, 1, 2, 3)
Bankoski, et al. Informational [Page 53]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
The exact algorithm is as follows:
---- Begin code block --------------------------------------
void TMpred(
Pixel b[8][8], /* chroma (U or V) prediction block */
const Pixel A[8], /* row of already-constructed pixels
above block */
const Pixel L[8], /* column of "" just to the left of
block */
const Pixel P /* pixel just to the left of A and
above L*/
) {
int r = 0; /* row */
do {
int c = 0; /* column */
do {
b[r][c] = clamp255(L[r]+ A[c] - P);
} while (++c < 8);
} while (++r < 8);
}
---- End code block ----------------------------------------
Note that the process could equivalently be described as propagating
the vertical differences between pixels in L (starting from P), using
the pixels from A to start each column.
An implementation of chroma intra-prediction may be found in the
reference decoder file predict.c (Section 20.14).
Unlike DC_PRED, for macroblocks on the top row or left edge, TM_PRED
does use the out-of-bounds values of 127 and 129 (respectively)
defined for V_PRED and H_PRED.
12.3. Luma Prediction
The prediction processes for the first four 16x16 luma modes
(DC_PRED, V_PRED, H_PRED, and TM_PRED) are essentially identical to
the corresponding chroma prediction processes described above, the
only difference being that we are predicting a single 16x16 luma
block instead of two 8x8 chroma blocks.
Thus, the row "A" and column "L" here contain 16 pixels, the DC
prediction is calculated using 16 or 32 pixels (and shf is 4 or 5),
and we of course fill the entire prediction buffer, that is, 16 rows
(or columns) containing 16 pixels each. The reference implementation
of 16x16 luma prediction is also in predict.c.
Bankoski, et al. Informational [Page 54]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
In the remaining luma mode (B_PRED), each 4x4 Y subblock is
independently predicted using one of ten modes (listed, along with
their encodings, in Section 11).
Also, unlike the full-macroblock modes already described, some of the
subblock modes use prediction pixels above and to the right of the
current subblock. In detail, each 4x4 subblock "B" is predicted
using (at most) the 4-pixel column "L" immediately to the left of B
and the 8-pixel row "A" immediately above B, consisting of the 4
pixels above B followed by the 4 adjacent pixels above and to the
right of B, together with the single pixel "P" immediately to the
left of A (and immediately above L).
For the purpose of subblock intra-prediction, the pixels immediately
to the left and right of a pixel in a subblock are the same as the
pixels immediately to the left and right of the corresponding pixel
in the frame buffer "F". Vertical offsets behave similarly: The
above row A lies immediately above B in F, and the adjacent pixels in
the left column L are separated by a single row in F.
Because entire macroblocks (as opposed to their constituent
subblocks) are reconstructed in raster-scan order, for subblocks
lying along the right edge (and not along the top row) of the current
macroblock, the four "extra" prediction pixels in A above and to the
right of B have not yet actually been constructed.
Subblocks 7, 11, and 15 are affected. All three of these subblocks
use the same extra pixels as does subblock 3 (at the upper right
corner of the macroblock), namely the 4 pixels immediately above and
to the right of subblock 3. Writing (R,C) for a frame buffer
position offset from the upper left corner of the current macroblock
by R rows and C columns, the extra pixels for all the right-edge
subblocks (3, 7, 11, and 15) are at positions (-1,16), (-1,17),
(-1,18), and (-1,19). For the rightmost macroblock in each
macroblock row except the top row, the extra pixels shall use the
same value as the pixel at position (-1,15), which is the rightmost
visible pixel on the line immediately above the macroblock row. For
the top macroblock row, all the extra pixels assume a value of 127.
The details of the prediction modes are most easily described in
code.
Bankoski, et al. Informational [Page 55]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
---- Begin code block --------------------------------------
/* Result pixels are often averages of two or three predictor
pixels. The following subroutines are used to calculate
these averages. Because the arguments are valid pixels, no
clamping is necessary. An actual implementation would
probably use inline functions or macros. */
/* Compute weighted average centered at y w/adjacent x, z */
Pixel avg3(Pixel x, Pixel y, Pixel z) {
return (x + y + y + z + 2) >> 2;}
/* Weighted average of 3 adjacent pixels centered at p */
Pixel avg3p(const Pixel *p) { return avg3(p[-1], p[0], p[1]);}
/* Simple average of x and y */
Pixel avg2(Pixel x, Pixel y) { return (x + y + 1) >> 1;}
/* Average of p[0] and p[1] may be considered to be a synthetic
pixel lying between the two, that is, one half-step past p. */
Pixel avg2p(const Pixel *p) { return avg2(p[0], p[1]);}
void subblock_intra_predict(
Pixel B[4][4], /* Y subblock prediction buffer */
const Pixel *A, /* A[0]...A[7] = above row, A[-1] = P */
const Pixel *L, /* L[0]...L[3] = left column, L[-1] = P */
intra_bmode mode /* enum is in Section 11.2 */
) {
Pixel E[9]; /* 9 already-constructed edge pixels */
E[0] = L[3]; E[1] = L[2]; E[2] = L[1]; E[3] = L[0];
E[4] = A[-1]; /* == L[-1] == P */
E[5] = A[0]; E[6] = A[1]; E[7] = A[2]; E[8] = A[3];
switch(mode) {
/* First four modes are similar to corresponding
full-block modes. */
case B_DC_PRED:
{
int v = 4; /* DC sum/avg, 4 is rounding adjustment */
int i = 0; do { v += A[i] + L[i];} while (++i < 4);
v >>= 3; /* averaging 8 pixels */
i = 0; do { /* fill prediction buffer with constant DC
value */
Bankoski, et al. Informational [Page 56]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
int j = 0; do { B[i][j] = v;} while (++j < 4);
} while (++i < 4);
break;
}
case B_TM_PRED: /* just like 16x16 TM_PRED */
{
int r = 0; do {
int c = 0; do {
B[r][c] = clamp255(L[r] + A[c] - A[-1]);
} while (++c < 4);
} while (++r < 4);
break;
}
case B_VE_PRED: /* like 16x16 V_PRED except using averages */
{
int c = 0; do { /* all 4 rows = smoothed top row */
B[0][c] = B[1][c] = B[2][c] = B[3][c] = avg3p(A + c);
} while (++c < 4);
break;
}
case B_HE_PRED: /* like 16x16 H_PRED except using averages */
{
/* Bottom row is exceptional because L[4] does not exist */
int v = avg3(L[2], L[3], L[3]);
int r = 3; while (1) { /* all 4 columns = smoothed left
column */
B[r][0] = B[r][1] = B[r][2] = B[r][3] = v;
if (--r < 0)
break;
v = avg3p(L + r); /* upper 3 rows use average of
3 pixels */
}
break;
}
/* The remaining six "diagonal" modes subdivide the
prediction buffer into diagonal lines. All the pixels
on each line are assigned the same value; this value is
(a smoothed or synthetic version of) an
already-constructed predictor value lying on the same
line. For clarity, in the comments, we express the
positions of these predictor pixels relative to the
upper left corner of the destination array B.
Bankoski, et al. Informational [Page 57]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
These modes are unique to subblock prediction and have
no full-block analogs. The first two use lines at
+|- 45 degrees from horizontal (or, equivalently,
vertical), that is, lines whose slopes are +|- 1. */
case B_LD_PRED: /* southwest (left and down) step =
(-1, 1) or (1,-1) */
/* avg3p(A + j) is the "smoothed" pixel at (-1,j) */
B[0][0] = avg3p(A + 1);
B[0][1] = B[1][0] = avg3p(A + 2);
B[0][2] = B[1][1] = B[2][0] = avg3p(A + 3);
B[0][3] = B[1][2] = B[2][1] = B[3][0] = avg3p(A + 4);
B[1][3] = B[2][2] = B[3][1] = avg3p(A + 5);
B[2][3] = B[3][2] = avg3p(A + 6);
B[3][3] = avg3(A[6], A[7], A[7]); /* A[8] does not exist */
break;
case B_RD_PRED: /* southeast (right and down) step =
(1,1) or (-1,-1) */
B[3][0] = avg3p(E + 1); /* predictor is from (2, -1) */
B[3][1] = B[2][0] = avg3p(E + 2); /* (1, -1) */
B[3][2] = B[2][1] = B[1][0] = avg3p(E + 3); /* (0, -1) */
B[3][3] = B[2][2] = B[1][1] = B[0][0] =
avg3p(E + 4); /* (-1, -1) */
B[2][3] = B[1][2] = B[0][1] = avg3p(E + 5); /* (-1, 0) */
B[1][3] = B[0][2] = avg3p(E + 6); /* (-1, 1) */
B[0][3] = avg3p(E + 7); /* (-1, 2) */
break;
/* The remaining 4 diagonal modes use lines whose slopes are
+|- 2 and +|- 1/2. The angles of these lines are roughly
+|- 27 degrees from horizontal or vertical.
Unlike the 45 degree diagonals, here we often need to
"synthesize" predictor pixels midway between two actual
predictors using avg2p(p), which we think of as returning
the pixel "at" p[1/2]. */
case B_VR_PRED: /* SSE (vertical right) step =
(2,1) or (-2,-1) */
B[3][0] = avg3p(E + 2); /* predictor is from (1, -1) */
B[2][0] = avg3p(E + 3); /* (0, -1) */
B[3][1] = B[1][0] = avg3p(E + 4); /* (-1, -1) */
B[2][1] = B[0][0] = avg2p(E + 4); /* (-1, -1/2) */
B[3][2] = B[1][1] = avg3p(E + 5); /* (-1, 0) */
B[2][2] = B[0][1] = avg2p(E + 5); /* (-1, 1/2) */
B[3][3] = B[1][2] = avg3p(E + 6); /* (-1, 1) */
B[2][3] = B[0][2] = avg2p(E + 6); /* (-1, 3/2) */
Bankoski, et al. Informational [Page 58]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
B[1][3] = avg3p(E + 7); /* (-1, 2) */
B[0][3] = avg2p(E + 7); /* (-1, 5/2) */
break;
case B_VL_PRED: /* SSW (vertical left) step =
(2,-1) or (-2,1) */
B[0][0] = avg2p(A); /* predictor is from (-1, 1/2) */
B[1][0] = avg3p(A + 1); /* (-1, 1) */
B[2][0] = B[0][1] = avg2p(A + 1); /* (-1, 3/2) */
B[1][1] = B[3][0] = avg3p(A + 2); /* (-1, 2) */
B[2][1] = B[0][2] = avg2p(A + 2); /* (-1, 5/2) */
B[3][1] = B[1][2] = avg3p(A + 3); /* (-1, 3) */
B[2][2] = B[0][3] = avg2p(A + 3); /* (-1, 7/2) */
B[3][2] = B[1][3] = avg3p(A + 4); /* (-1, 4) */
/* Last two values do not strictly follow the pattern. */
B[2][3] = avg3p(A + 5); /* (-1, 5) [avg2p(A + 4) =
(-1,9/2)] */
B[3][3] = avg3p(A + 6); /* (-1, 6) [avg3p(A + 5) =
(-1,5)] */
break;
case B_HD_PRED: /* ESE (horizontal down) step =
(1,2) or (-1,-2) */
B[3][0] = avg2p(E); /* predictor is from (5/2, -1) */
B[3][1] = avg3p(E + 1); /* (2, -1) */
B[2][0] = B[3][2] = svg2p(E + 1); /* ( 3/2, -1) */
B[2][1] = B[3][3] = avg3p(E + 2); /* ( 1, -1) */
B[2][2] = B[1][0] = avg2p(E + 2); /* ( 1/2, -1) */
B[2][3] = B[1][1] = avg3p(E + 3); /* ( 0, -1) */
B[1][2] = B[0][0] = avg2p(E + 3); /* (-1/2, -1) */
B[1][3] = B[0][1] = avg3p(E + 4); /* ( -1, -1) */
B[0][2] = avg3p(E + 5); /* (-1, 0) */
B[0][3] = avg3p(E + 6); /* (-1, 1) */
break;
case B_HU_PRED: /* ENE (horizontal up) step = (1,-2)
or (-1,2) */
B[0][0] = avg2p(L); /* predictor is from (1/2, -1) */
B[0][1] = avg3p(L + 1); /* (1, -1) */
B[0][2] = B[1][0] = avg2p(L + 1); /* (3/2, -1) */
B[0][3] = B[1][1] = avg3p(L + 2); /* ( 2, -1) */
B[1][2] = B[2][0] = avg2p(L + 2); /* (5/2, -1) */
B[1][3] = B[2][1] = avg3(L[2], L[3], L[3]); /* (3, -1) */
Bankoski, et al. Informational [Page 59]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/* Not possible to follow pattern for much of the bottom
row because no (nearby) already-constructed pixels lie
on the diagonals in question. */
B[2][2] = B[2][3] = B[3][0] = B[3][1] = B[3][2] = B[3][3]
= L[3];
}
}
---- End code block ----------------------------------------
The reference decoder implementation of subblock intra-prediction may
be found in predict.c (Section 20.14).
13. DCT Coefficient Decoding
The second data partition consists of an encoding of the quantized
DCT (and WHT) coefficients of the residue signal. As discussed in
the format overview (Section 2), for each macroblock, the residue is
added to the (intra- or inter-generated) prediction buffer to produce
the final (except for loop filtering) reconstructed macroblock.
VP8 works exclusively with 4x4 DCTs and WHTs, applied to the 24 (or
25 with the Y2 subblock) 4x4 subblocks of a macroblock. The ordering
of macroblocks within any of the "residue" partitions in general
follows the same raster scan as used in the first "prediction"
partition.
For all intra- and inter-prediction modes apart from B_PRED (intra:
whose Y subblocks are independently predicted) and SPLITMV (inter),
each macroblock's residue record begins with the Y2 component of the
residue, coded using a WHT. B_PRED and SPLITMV coded macroblocks
omit this WHT and specify the 0th DCT coefficient in each of the 16 Y
subblocks.
After the optional Y2 block, the residue record continues with 16
DCTs for the Y subblocks, followed by 4 DCTs for the U subblocks,
ending with 4 DCTs for the V subblocks. The subblocks occur in the
usual order.
The DCTs and WHT are tree-coded using a 12-element alphabet whose
members we call "tokens". Except for the end-of-block token (which
sets the remaining subblock coefficients to zero and is followed by
the next block), each token (sometimes augmented with data
immediately following the token) specifies the value of the single
coefficient at the current (implicit) position and is followed by a
token applying to the next (implicit) position.
Bankoski, et al. Informational [Page 60]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
For all the Y and chroma subblocks, the ordering of the coefficients
follows a so-called zig-zag order. DCTs begin at coefficient 1 if Y2
is present, and begin at coefficient 0 if Y2 is absent. The WHT for
a Y2 subblock always begins at coefficient 0.
13.1. Macroblock without Non-Zero Coefficient Values
If the flag within macroblock (MB) MODE_INFO indicates that a
macroblock does not have any non-zero coefficients, the decoding
process of DCT coefficients is skipped for the macroblock.
13.2. Coding of Individual Coefficient Values
The coding of coefficient tokens is the same for the DCT and WHT, and
for the remainder of this section "DCT" should be taken to mean
either DCT or WHT.
All tokens (except end-of-block) specify either a single unsigned
value or a range of unsigned values (immediately) followed by a
simple probabilistic encoding of the offset of the value from the
base of that range.
Non-zero values (of either type) are then followed by a flag
indicating the sign of the coded value (negative if 1, positive
if 0).
Below are the tokens and decoding tree.
---- Begin code block --------------------------------------
typedef enum
{
DCT_0, /* value 0 */
DCT_1, /* 1 */
DCT_2, /* 2 */
DCT_3, /* 3 */
DCT_4, /* 4 */
dct_cat1, /* range 5 - 6 (size 2) */
dct_cat2, /* 7 - 10 (4) */
dct_cat3, /* 11 - 18 (8) */
dct_cat4, /* 19 - 34 (16) */
dct_cat5, /* 35 - 66 (32) */
dct_cat6, /* 67 - 2048 (1982) */
dct_eob, /* end of block */
num_dct_tokens /* 12 */
}
dct_token;
Bankoski, et al. Informational [Page 61]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
const tree_index coeff_tree [2 * (num_dct_tokens - 1)] =
{
-dct_eob, 2, /* eob = "0" */
-DCT_0, 4, /* 0 = "10" */
-DCT_1, 6, /* 1 = "110" */
8, 12,
-DCT_2, 10, /* 2 = "11100" */
-DCT_3, -DCT_4, /* 3 = "111010", 4 = "111011" */
14, 16,
-dct_cat1, -dct_cat2, /* cat1 = "111100",
cat2 = "111101" */
18, 20,
-dct_cat3, -dct_cat4, /* cat3 = "1111100",
cat4 = "1111101" */
-dct_cat5, -dct_cat6 /* cat4 = "1111110",
cat4 = "1111111" */
};
---- End code block ----------------------------------------
In general, all DCT coefficients are decoded using the same tree.
However, if the preceding coefficient is a DCT_0, decoding will skip
the first branch, since it is not possible for dct_eob to follow a
DCT_0.
The tokens dct_cat1 ... dct_cat6 specify ranges of unsigned values,
the value within the range being formed by adding an unsigned offset
(whose width is 1, 2, 3, 4, 5, or 11 bits, respectively) to the base
of the range, using the following algorithm and fixed probability
tables.
Bankoski, et al. Informational [Page 62]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
---- Begin code block --------------------------------------
uint DCTextra(bool_decoder *d, const Prob *p)
{
uint v = 0;
do { v += v + read_bool(d, *p);} while (*++p);
return v;
}
const Prob Pcat1[] = { 159, 0};
const Prob Pcat2[] = { 165, 145, 0};
const Prob Pcat3[] = { 173, 148, 140, 0};
const Prob Pcat4[] = { 176, 155, 140, 135, 0};
const Prob Pcat5[] = { 180, 157, 141, 134, 130, 0};
const Prob Pcat6[] =
{ 254, 254, 243, 230, 196, 177, 153, 140, 133, 130, 129, 0};
---- End code block ----------------------------------------
If v -- the unsigned value decoded using the coefficient tree,
possibly augmented by the process above -- is non-zero, its sign is
set by simply reading a flag:
---- Begin code block --------------------------------------
if (read_bool(d, 128))
v = -v;
---- End code block ----------------------------------------
13.3. Token Probabilities
The probability specification for the token tree (unlike that for the
"extra bits" described above) is rather involved. It uses three
pieces of context to index a large probability table, the contents of
which may be incrementally modified in the frame header. The full
(non-constant) probability table is laid out as follows.
---- Begin code block --------------------------------------
Prob coeff_probs [4] [8] [3] [num_dct_tokens-1];
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 63]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
Working from the outside in, the outermost dimension is indexed by
the type of plane being decoded:
o 0 - Y beginning at coefficient 1 (i.e., Y after Y2)
o 1 - Y2
o 2 - U or V
o 3 - Y beginning at coefficient 0 (i.e., Y in the absence of Y2).
The next dimension is selected by the position of the coefficient
being decoded. That position, c, steps by ones up to 15, starting
from zero for block types 1, 2, or 3 and starting from one for block
type 0. The second array index is then
---- Begin code block --------------------------------------
coeff_bands [c]
---- End code block ----------------------------------------
Where:
---- Begin code block --------------------------------------
const int coeff_bands [16] = {
0, 1, 2, 3, 6, 4, 5, 6, 6, 6, 6, 6, 6, 6, 6, 7
};
---- End code block ----------------------------------------
is a fixed mapping of position to "band".
The third dimension is the trickiest. Roughly speaking, it measures
the "local complexity" or extent to which nearby coefficients are
non-zero.
For the first coefficient (DC, unless the block type is 0), we
consider the (already encoded) blocks within the same plane (Y2, Y,
U, or V) above and to the left of the current block. The context
index is then the number (0, 1, or 2) of these blocks that had at
least one non-zero coefficient in their residue record. Specifically
for Y2, because macroblocks above and to the left may or may not have
a Y2 block, the block above is determined by the most recent
macroblock in the same column that has a Y2 block, and the block to
the left is determined by the most recent macroblock in the same row
that has a Y2 block.
Bankoski, et al. Informational [Page 64]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
Beyond the first coefficient, the context index is determined by the
absolute value of the most recently decoded coefficient (necessarily
within the current block) and is 0 if the last coefficient was a
zero, 1 if it was plus or minus one, and 2 if its absolute value
exceeded one.
Note that the intuitive meaning of this measure changes as
coefficients are decoded. For example, prior to the first token, a
zero means that the neighbors are empty, suggesting that the current
block may also be empty. After the first token, because an end-of-
block token must have at least one non-zero value before it, a zero
means that we just decoded a zero and hence guarantees that a
non-zero coefficient will appear later in this block. However, this
shift in meaning is perfectly okay because the complete context
depends also on the coefficient band (and since band 0 is occupied
exclusively by position 0).
As with other contexts used by VP8, the "neighboring block" context
described here needs a special definition for subblocks lying along
the top row or left edge of the frame. These "non-existent"
predictors above and to the left of the image are simply taken to be
empty -- that is, taken to contain no non-zero coefficients.
The residue decoding of each macroblock then requires, in each of two
directions (above and to the left), an aggregate coefficient
predictor consisting of a single Y2 predictor, two predictors for
each of U and V, and four predictors for Y. In accordance with the
scan-ordering of macroblocks, a decoder needs to maintain a single
"left" aggregate predictor and a row of "above" aggregate predictors.
Before decoding any residue, these maintained predictors may simply
be cleared, in compliance with the definition of "non-existent"
prediction. After each block is decoded, the two predictors
referenced by the block are replaced with the (empty or non-empty)
state of the block, in preparation for the later decoding of the
blocks below and to the right of the block just decoded.
The fourth, and final, dimension of the token probability array is of
course indexed by (half) the position in the token tree structure, as
are all tree probability arrays.
The pseudocode below illustrates the decoding process. Note that
criteria, functions, etc. delimited with ** are either dependent on
decoder architecture or are elaborated on elsewhere in this document.
Bankoski, et al. Informational [Page 65]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
---- Begin code block --------------------------------------
int block[16] = { 0 }; /* current 4x4 block coeffs */
int firstCoeff = 0;
int plane;
int ctx2;
int ctx3 = 0; /* the 3rd context referred to in above description */
Prob *probTable;
int token;
int sign;
int absValue;
int extraBits;
bool prevCoeffWasZero = false;
bool currentBlockHasCoeffs = false;
/* base coeff abs values per each category, elem #0 is
DCT_VAL_CATEGORY1, * #1 is DCT_VAL_CATEGORY2, etc. */
int categoryBase[6] = { 5, 7, 11, 19, 35, 67 };
/* Determine plane to use */
if ( **current_block_is_Y2_block** ) plane = 0;
else if ( **current_block_is_chroma** ) plane = 2;
else if ( **current_macroblock_has_Y2** ) plane = 1;
else plane = 3;
/* For luma blocks of a "Y2 macroblock" we skip coeff index #0 */
if ( plane == 1 )
firstCoeff++;
/* Determine whether neighbor 4x4 blocks have coefficients.
This is dependent on the plane we are currently decoding;
i.e., we check only coefficients from the same plane as the
current block. */
if ( **left_neighbor_block_has_coefficients(plane)** )
ctx3++;
if ( **above_neighbor_block_has_coefficients(plane)** )
ctx3++;
for( i = firstCoeff; i < 16; ++i )
{
ctx2 = coeff_bands[i];
probTable = coeff_probs[plane][ctx2][ctx3];
/* skip first code (dct_eob) if previous token was DCT_0 */
if ( prevCoeffWasZero )
token = treed_read ( d, **coeff_tree_without_eob**,
probTable );
else
token = treed_read ( d, coeff_tree, probTable );
Bankoski, et al. Informational [Page 66]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
if ( token == dct_eob )
break;
if ( token != DCT_0 )
{
currentBlockHasCoeffs = true;
if ( **token_has_extra_bits(token)** )
{
extraBits = DCTextra( token );
absValue =
categoryBase[**token_to_cat_index(token)**] +
extraBits;
}
else
{
absValue = **token_to_abs_value(token)**;
}
sign = read_bool(d, 128);
block[i] = sign ? -absValue : absValue;
}
else
{
absValue = 0;
}
/* Set contexts and stuff for next coeff */
if ( absValue == 0 ) ctx3 = 0;
else if ( absValue == 1 ) ctx3 = 1;
else ctx3 = 2;
prevCoeffWasZero = true;
}
/* Store current block status to decoder internals */
**block_has_coefficients[currentMb][currentBlock]** =
currentBlockHasCoeffs;
---- End code block ----------------------------------------
While we have in fact completely described the coefficient decoding
procedure, the reader will probably find it helpful to consult the
reference implementation, which can be found in the file tokens.c
(Section 20.16).
Bankoski, et al. Informational [Page 67]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
13.4. Token Probability Updates
As mentioned above, the token-decoding probabilities may change from
frame to frame. After detection of a key frame, they are of course
set to their defaults as shown in Section 13.5; this must occur
before decoding the remainder of the header, as both key frames and
interframes may adjust these probabilities.
The layout and semantics of the coefficient probability update record
(Section I of the frame header) are straightforward. For each
position in the coeff_probs array there occurs a fixed-probability
bool indicating whether or not the corresponding probability should
be updated. If the bool is true, there follows a P(8) replacing that
probability. Note that updates are cumulative; that is, a
probability updated on one frame is in effect for all ensuing frames
until the next key frame, or until the probability is explicitly
updated by another frame.
The algorithm to effect the foregoing is simple:
---- Begin code block --------------------------------------
int i = 0; do {
int j = 0; do {
int k = 0; do {
int t = 0; do {
if (read_bool(d, coeff_update_probs [i] [j] [k] [t]))
coeff_probs [i] [j] [k] [t] = read_literal(d, 8);
} while (++t < num_dct_tokens - 1);
} while (++k < 3);
} while (++j < 8);
} while (++i < 4);
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 68]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
The (constant) update probabilities are as follows:
---- Begin code block --------------------------------------
const Prob coeff_update_probs [4] [8] [3] [num_dct_tokens-1] =
{
{
{
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 176, 246, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 223, 241, 252, 255, 255, 255, 255, 255, 255, 255, 255},
{ 249, 253, 253, 255, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 244, 252, 255, 255, 255, 255, 255, 255, 255, 255},
{ 234, 254, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{ 253, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 246, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{ 239, 253, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{ 254, 255, 254, 255, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 248, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{ 251, 255, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 253, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{ 251, 254, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{ 254, 255, 254, 255, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 254, 253, 255, 254, 255, 255, 255, 255, 255, 255},
{ 250, 255, 254, 255, 254, 255, 255, 255, 255, 255, 255},
{ 254, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255}
}
},
Bankoski, et al. Informational [Page 69]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{
{
{ 217, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 225, 252, 241, 253, 255, 255, 254, 255, 255, 255, 255},
{ 234, 250, 241, 250, 253, 255, 253, 254, 255, 255, 255}
},
{
{ 255, 254, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 223, 254, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{ 238, 253, 254, 254, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 248, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{ 249, 254, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 253, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 247, 254, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 253, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{ 252, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 254, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{ 253, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 254, 253, 255, 255, 255, 255, 255, 255, 255, 255},
{ 250, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 254, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255}
}
},
{
{
{ 186, 251, 250, 255, 255, 255, 255, 255, 255, 255, 255},
{ 234, 251, 244, 254, 255, 255, 255, 255, 255, 255, 255},
{ 251, 251, 243, 253, 254, 255, 254, 255, 255, 255, 255}
},
Bankoski, et al. Informational [Page 70]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{
{ 255, 253, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{ 236, 253, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{ 251, 253, 253, 254, 254, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 254, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{ 254, 254, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 254, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 254, 254, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 254, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 254, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255}
}
},
{
{
{ 248, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 250, 254, 252, 254, 255, 255, 255, 255, 255, 255, 255},
{ 248, 254, 249, 253, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 253, 253, 255, 255, 255, 255, 255, 255, 255, 255},
{ 246, 253, 253, 255, 255, 255, 255, 255, 255, 255, 255},
{ 252, 254, 251, 254, 254, 255, 255, 255, 255, 255, 255}
},
Bankoski, et al. Informational [Page 71]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{
{ 255, 254, 252, 255, 255, 255, 255, 255, 255, 255, 255},
{ 248, 254, 253, 255, 255, 255, 255, 255, 255, 255, 255},
{ 253, 255, 254, 254, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 251, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{ 245, 251, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{ 253, 253, 254, 255, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 251, 253, 255, 255, 255, 255, 255, 255, 255, 255},
{ 252, 253, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{ 255, 254, 255, 255, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 252, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 249, 255, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{ 255, 255, 254, 255, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 255, 253, 255, 255, 255, 255, 255, 255, 255, 255},
{ 250, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255}
},
{
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 254, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{ 255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255}
}
}
};
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 72]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
13.5. Default Token Probability Table
The default token probabilities are as follows.
---- Begin code block --------------------------------------
const Prob default_coeff_probs [4] [8] [3] [num_dct_tokens - 1] =
{
{
{
{ 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128},
{ 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128},
{ 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128}
},
{
{ 253, 136, 254, 255, 228, 219, 128, 128, 128, 128, 128},
{ 189, 129, 242, 255, 227, 213, 255, 219, 128, 128, 128},
{ 106, 126, 227, 252, 214, 209, 255, 255, 128, 128, 128}
},
{
{ 1, 98, 248, 255, 236, 226, 255, 255, 128, 128, 128},
{ 181, 133, 238, 254, 221, 234, 255, 154, 128, 128, 128},
{ 78, 134, 202, 247, 198, 180, 255, 219, 128, 128, 128}
},
{
{ 1, 185, 249, 255, 243, 255, 128, 128, 128, 128, 128},
{ 184, 150, 247, 255, 236, 224, 128, 128, 128, 128, 128},
{ 77, 110, 216, 255, 236, 230, 128, 128, 128, 128, 128}
},
{
{ 1, 101, 251, 255, 241, 255, 128, 128, 128, 128, 128},
{ 170, 139, 241, 252, 236, 209, 255, 255, 128, 128, 128},
{ 37, 116, 196, 243, 228, 255, 255, 255, 128, 128, 128}
},
{
{ 1, 204, 254, 255, 245, 255, 128, 128, 128, 128, 128},
{ 207, 160, 250, 255, 238, 128, 128, 128, 128, 128, 128},
{ 102, 103, 231, 255, 211, 171, 128, 128, 128, 128, 128}
},
{
{ 1, 152, 252, 255, 240, 255, 128, 128, 128, 128, 128},
{ 177, 135, 243, 255, 234, 225, 128, 128, 128, 128, 128},
{ 80, 129, 211, 255, 194, 224, 128, 128, 128, 128, 128}
},
Bankoski, et al. Informational [Page 73]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{
{ 1, 1, 255, 128, 128, 128, 128, 128, 128, 128, 128},
{ 246, 1, 255, 128, 128, 128, 128, 128, 128, 128, 128},
{ 255, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128}
}
},
{
{
{ 198, 35, 237, 223, 193, 187, 162, 160, 145, 155, 62},
{ 131, 45, 198, 221, 172, 176, 220, 157, 252, 221, 1},
{ 68, 47, 146, 208, 149, 167, 221, 162, 255, 223, 128}
},
{
{ 1, 149, 241, 255, 221, 224, 255, 255, 128, 128, 128},
{ 184, 141, 234, 253, 222, 220, 255, 199, 128, 128, 128},
{ 81, 99, 181, 242, 176, 190, 249, 202, 255, 255, 128}
},
{
{ 1, 129, 232, 253, 214, 197, 242, 196, 255, 255, 128},
{ 99, 121, 210, 250, 201, 198, 255, 202, 128, 128, 128},
{ 23, 91, 163, 242, 170, 187, 247, 210, 255, 255, 128}
},
{
{ 1, 200, 246, 255, 234, 255, 128, 128, 128, 128, 128},
{ 109, 178, 241, 255, 231, 245, 255, 255, 128, 128, 128},
{ 44, 130, 201, 253, 205, 192, 255, 255, 128, 128, 128}
},
{
{ 1, 132, 239, 251, 219, 209, 255, 165, 128, 128, 128},
{ 94, 136, 225, 251, 218, 190, 255, 255, 128, 128, 128},
{ 22, 100, 174, 245, 186, 161, 255, 199, 128, 128, 128}
},
{
{ 1, 182, 249, 255, 232, 235, 128, 128, 128, 128, 128},
{ 124, 143, 241, 255, 227, 234, 128, 128, 128, 128, 128},
{ 35, 77, 181, 251, 193, 211, 255, 205, 128, 128, 128}
},
{
{ 1, 157, 247, 255, 236, 231, 255, 255, 128, 128, 128},
{ 121, 141, 235, 255, 225, 227, 255, 255, 128, 128, 128},
{ 45, 99, 188, 251, 195, 217, 255, 224, 128, 128, 128}
},
{
{ 1, 1, 251, 255, 213, 255, 128, 128, 128, 128, 128},
{ 203, 1, 248, 255, 255, 128, 128, 128, 128, 128, 128},
{ 137, 1, 177, 255, 224, 255, 128, 128, 128, 128, 128}
}
},
Bankoski, et al. Informational [Page 74]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{
{
{ 253, 9, 248, 251, 207, 208, 255, 192, 128, 128, 128},
{ 175, 13, 224, 243, 193, 185, 249, 198, 255, 255, 128},
{ 73, 17, 171, 221, 161, 179, 236, 167, 255, 234, 128}
},
{
{ 1, 95, 247, 253, 212, 183, 255, 255, 128, 128, 128},
{ 239, 90, 244, 250, 211, 209, 255, 255, 128, 128, 128},
{ 155, 77, 195, 248, 188, 195, 255, 255, 128, 128, 128}
},
{
{ 1, 24, 239, 251, 218, 219, 255, 205, 128, 128, 128},
{ 201, 51, 219, 255, 196, 186, 128, 128, 128, 128, 128},
{ 69, 46, 190, 239, 201, 218, 255, 228, 128, 128, 128}
},
{
{ 1, 191, 251, 255, 255, 128, 128, 128, 128, 128, 128},
{ 223, 165, 249, 255, 213, 255, 128, 128, 128, 128, 128},
{ 141, 124, 248, 255, 255, 128, 128, 128, 128, 128, 128}
},
{
{ 1, 16, 248, 255, 255, 128, 128, 128, 128, 128, 128},
{ 190, 36, 230, 255, 236, 255, 128, 128, 128, 128, 128},
{ 149, 1, 255, 128, 128, 128, 128, 128, 128, 128, 128}
},
{
{ 1, 226, 255, 128, 128, 128, 128, 128, 128, 128, 128},
{ 247, 192, 255, 128, 128, 128, 128, 128, 128, 128, 128},
{ 240, 128, 255, 128, 128, 128, 128, 128, 128, 128, 128}
},
{
{ 1, 134, 252, 255, 255, 128, 128, 128, 128, 128, 128},
{ 213, 62, 250, 255, 255, 128, 128, 128, 128, 128, 128},
{ 55, 93, 255, 128, 128, 128, 128, 128, 128, 128, 128}
},
{
{ 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128},
{ 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128},
{ 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128}
}
},
{
{
{ 202, 24, 213, 235, 186, 191, 220, 160, 240, 175, 255},
{ 126, 38, 182, 232, 169, 184, 228, 174, 255, 187, 128},
{ 61, 46, 138, 219, 151, 178, 240, 170, 255, 216, 128}
},
Bankoski, et al. Informational [Page 75]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{
{ 1, 112, 230, 250, 199, 191, 247, 159, 255, 255, 128},
{ 166, 109, 228, 252, 211, 215, 255, 174, 128, 128, 128},
{ 39, 77, 162, 232, 172, 180, 245, 178, 255, 255, 128}
},
{
{ 1, 52, 220, 246, 198, 199, 249, 220, 255, 255, 128},
{ 124, 74, 191, 243, 183, 193, 250, 221, 255, 255, 128},
{ 24, 71, 130, 219, 154, 170, 243, 182, 255, 255, 128}
},
{
{ 1, 182, 225, 249, 219, 240, 255, 224, 128, 128, 128},
{ 149, 150, 226, 252, 216, 205, 255, 171, 128, 128, 128},
{ 28, 108, 170, 242, 183, 194, 254, 223, 255, 255, 128}
},
{
{ 1, 81, 230, 252, 204, 203, 255, 192, 128, 128, 128},
{ 123, 102, 209, 247, 188, 196, 255, 233, 128, 128, 128},
{ 20, 95, 153, 243, 164, 173, 255, 203, 128, 128, 128}
},
{
{ 1, 222, 248, 255, 216, 213, 128, 128, 128, 128, 128},
{ 168, 175, 246, 252, 235, 205, 255, 255, 128, 128, 128},
{ 47, 116, 215, 255, 211, 212, 255, 255, 128, 128, 128}
},
{
{ 1, 121, 236, 253, 212, 214, 255, 255, 128, 128, 128},
{ 141, 84, 213, 252, 201, 202, 255, 219, 128, 128, 128},
{ 42, 80, 160, 240, 162, 185, 255, 205, 128, 128, 128}
},
{
{ 1, 1, 255, 128, 128, 128, 128, 128, 128, 128, 128},
{ 244, 1, 255, 128, 128, 128, 128, 128, 128, 128, 128},
{ 238, 1, 255, 128, 128, 128, 128, 128, 128, 128, 128}
}
}
};
---- End code block ----------------------------------------
14. DCT and WHT Inversion and Macroblock Reconstruction
14.1. Dequantization
After decoding the DCTs/WHTs as described above, each (quantized)
coefficient in each subblock is multiplied by one of six
dequantization factors, the choice of factor depending on the plane
(Y2, Y, or chroma) and position (DC = coefficient zero, AC = any
Bankoski, et al. Informational [Page 76]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
other coefficient). If the current macroblock has overridden the
quantizer level (as described in Section 10), then the six factors
are looked up from two dequantization tables with appropriate scaling
and clamping using the single index supplied by the override.
Otherwise, the frame-level dequantization factors (as described in
Section 9.6) are used. In either case, the multiplies are computed
and stored using 16-bit signed integers.
The two dequantization tables, which may also be found in the
reference decoder file dequant_data.h (Section 20.3), are as follows.
---- Begin code block --------------------------------------
static const int dc_qlookup[QINDEX_RANGE] =
{
4, 5, 6, 7, 8, 9, 10, 10, 11, 12, 13, 14, 15,
16, 17, 17, 18, 19, 20, 20, 21, 21, 22, 22, 23, 23,
24, 25, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35,
36, 37, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 46,
47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59,
60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72,
73, 74, 75, 76, 76, 77, 78, 79, 80, 81, 82, 83, 84,
85, 86, 87, 88, 89, 91, 93, 95, 96, 98, 100, 101, 102,
104, 106, 108, 110, 112, 114, 116, 118, 122, 124, 126, 128, 130,
132, 134, 136, 138, 140, 143, 145, 148, 151, 154, 157,
};
static const int ac_qlookup[QINDEX_RANGE] =
{
4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16,
17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29,
30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42,
43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55,
56, 57, 58, 60, 62, 64, 66, 68, 70, 72, 74, 76, 78,
80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 100, 102, 104,
106, 108, 110, 112, 114, 116, 119, 122, 125, 128, 131, 134, 137,
140, 143, 146, 149, 152, 155, 158, 161, 164, 167, 170, 173, 177,
181, 185, 189, 193, 197, 201, 205, 209, 213, 217, 221, 225, 229,
234, 239, 245, 249, 254, 259, 264, 269, 274, 279, 284,
};
---- End code block ----------------------------------------
Lookup values from the above two tables are directly used in the DC
and AC coefficients in Y1, respectively. For Y2 and chroma, values
from the above tables undergo either scaling or clamping before the
multiplies. Details regarding these scaling and clamping processes
can be found in related lookup functions in dixie.c (Section 20.4).
Bankoski, et al. Informational [Page 77]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
14.2. Inverse Transforms
If the Y2 residue block exists (i.e., the macroblock luma mode is not
SPLITMV or B_PRED), it is inverted first (using the inverse WHT) and
the element of the result at row i, column j is used as the 0th
coefficient of the Y subblock at position (i, j), that is, the Y
subblock whose index is (i * 4) + j. As discussed in Section 13, if
the luma mode is B_PRED or SPLITMV, the 0th Y coefficients are part
of the residue signal for the subblocks themselves.
In either case, the inverse transforms for the sixteen Y subblocks
and eight chroma subblocks are computed next. All 24 of these
inversions are independent of each other; their results may (at least
conceptually) be stored in 24 separate 4x4 arrays.
As is done by the reference decoder, an implementation may wish to
represent the prediction and residue buffers as macroblock-sized
arrays (that is, a 16x16 Y buffer and two 8x8 chroma buffers).
Regarding the inverse DCT implementation given below, this requires a
simple adjustment to the address calculation for the resulting
residue pixels.
14.3. Implementation of the WHT Inversion
As previously discussed (see Sections 2 and 13), for macroblocks
encoded using prediction modes other than B_PRED and SPLITMV, the DC
values derived from the DCT transform on the 16 Y blocks are
collected to construct a 25th block of a macroblock (16 Y, 4 U, 4 V
constitute the 24 blocks). This 25th block is transformed using a
Walsh-Hadamard transform (WHT).
The inputs to the inverse WHT (that is, the dequantized
coefficients), the intermediate "horizontally detransformed" signal,
and the completely detransformed residue signal are all stored as
arrays of 16-bit signed integers.
Following the tradition of specifying bitstream format using the
decoding process, we specify the inverse WHT in the decoding process
using the following C-style source code:
Bankoski, et al. Informational [Page 78]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
---- Begin code block --------------------------------------
void vp8_short_inv_walsh4x4_c(short *input, short *output)
{
int i;
int a1, b1, c1, d1;
int a2, b2, c2, d2;
short *ip = input;
short *op = output;
int temp1, temp2;
for(i=0;i<4;i++)
{
a1 = ip[0] + ip[12];
b1 = ip[4] + ip[8];
c1 = ip[4] - ip[8];
d1 = ip[0] - ip[12];
op[0] = a1 + b1;
op[4] = c1 + d1;
op[8] = a1 - b1;
op[12]= d1 - c1;
ip++;
op++;
}
ip = output;
op = output;
for(i=0;i<4;i++)
{
a1 = ip[0] + ip[3];
b1 = ip[1] + ip[2];
c1 = ip[1] - ip[2];
d1 = ip[0] - ip[3];
a2 = a1 + b1;
b2 = c1 + d1;
c2 = a1 - b1;
d2 = d1 - c1;
Bankoski, et al. Informational [Page 79]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
op[0] = (a2+3)>>3;
op[1] = (b2+3)>>3;
op[2] = (c2+3)>>3;
op[3] = (d2+3)>>3;
ip+=4;
op+=4;
}
}
---- End code block ----------------------------------------
In the case that there is only one non-zero DC value in input, the
inverse transform can be simplified to the following:
---- Begin code block --------------------------------------
void vp8_short_inv_walsh4x4_1_c(short *input, short *output)
{
int i;
int a1;
short *op=output;
a1 = ((input[0] + 3)>>3);
for(i=0;i<4;i++)
{
op[0] = a1;
op[1] = a1;
op[2] = a1;
op[3] = a1;
op+=4;
}
}
---- End code block ----------------------------------------
It should be noted that a conforming decoder should implement the
inverse transform using exactly the same rounding to achieve bit-wise
matching output to the output of the process specified by the above
C source code.
The reference decoder WHT inversion may be found in the file
idct_add.c (Section 20.8).
Bankoski, et al. Informational [Page 80]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
14.4. Implementation of the DCT Inversion
All of the DCT inversions are computed in exactly the same way. In
principle, VP8 uses a classical 2-D inverse discrete cosine
transform, implemented as two passes of 1-D inverse DCT. The 1-D
inverse DCT was calculated using a similar algorithm to what was
described in [Loeffler]. However, the paper only provided the
8-point and 16-point version of the algorithms, which was adapted by
On2 to perform the 4-point 1-D DCT.
Accurate calculation of 1-D DCT of the above algorithm requires
infinite precision. VP8 of course can use only a finite-precision
approximation. Also, the inverse DCT used by VP8 takes care of
normalization of the standard unitary transform; that is, every
dequantized coefficient has roughly double the size of the
corresponding unitary coefficient. However, at all but the highest
datarates, the discrepancy between transmitted and ideal coefficients
is due almost entirely to (lossy) compression and not to errors
induced by finite-precision arithmetic.
The inputs to the inverse DCT (that is, the dequantized
coefficients), the intermediate "horizontally detransformed" signal,
and the completely detransformed residue signal are all stored as
arrays of 16-bit signed integers. The details of the computation are
as follows.
It should also be noted that this implementation makes use of the
16-bit fixed-point version of two multiplication constants:
sqrt(2) * cos (pi/8)
sqrt(2) * sin (pi/8)
Because the first constant is bigger than 1, to maintain the same
16-bit fixed-point precision as the second one, we make use of the
fact that
x * a = x + x*(a-1)
therefore
x * sqrt(2) * cos (pi/8) = x + x * (sqrt(2) * cos(pi/8)-1)
Bankoski, et al. Informational [Page 81]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
---- Begin code block --------------------------------------
/* IDCT implementation */
static const int cospi8sqrt2minus1=20091;
static const int sinpi8sqrt2 =35468;
void short_idct4x4llm_c(short *input, short *output, int pitch)
{
int i;
int a1, b1, c1, d1;
short *ip=input;
short *op=output;
int temp1, temp2;
int shortpitch = pitch>>1;
for(i=0;i<4;i++)
{
a1 = ip[0]+ip[8];
b1 = ip[0]-ip[8];
temp1 = (ip[4] * sinpi8sqrt2)>>16;
temp2 = ip[12]+((ip[12] * cospi8sqrt2minus1)>>16);
c1 = temp1 - temp2;
temp1 = ip[4] + ((ip[4] * cospi8sqrt2minus1)>>16);
temp2 = (ip[12] * sinpi8sqrt2)>>16;
d1 = temp1 + temp2;
op[shortpitch*0] = a1+d1;
op[shortpitch*3] = a1-d1;
op[shortpitch*1] = b1+c1;
op[shortpitch*2] = b1-c1;
ip++;
op++;
}
ip = output;
op = output;
for(i=0;i<4;i++)
{
a1 = ip[0]+ip[2];
b1 = ip[0]-ip[2];
temp1 = (ip[1] * sinpi8sqrt2)>>16;
temp2 = ip[3]+((ip[3] * cospi8sqrt2minus1)>>16);
c1 = temp1 - temp2;
temp1 = ip[1] + ((ip[1] * cospi8sqrt2minus1)>>16);
Bankoski, et al. Informational [Page 82]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
temp2 = (ip[3] * sinpi8sqrt2)>>16;
d1 = temp1 + temp2;
op[0] = (a1+d1+4)>>3;
op[3] = (a1-d1+4)>>3;
op[1] = (b1+c1+4)>>3;
op[2] = (b1-c1+4)>>3;
ip+=shortpitch;
op+=shortpitch;
}
}
---- End code block ----------------------------------------
The reference decoder DCT inversion may be found in the file
idct_add.c (Section 20.8).
14.5. Summation of Predictor and Residue
Finally, the prediction and residue signals are summed to form the
reconstructed macroblock, which, except for loop filtering (taken up
next), completes the decoding process.
The summing procedure is fairly straightforward, having only a couple
of details. The prediction and residue buffers are both arrays of
16-bit signed integers. Each individual (Y, U, and V pixel) result
is calculated first as a 32-bit sum of the prediction and residue,
and is then saturated to 8-bit unsigned range (using, say, the
clamp255 function defined above) before being stored as an 8-bit
unsigned pixel value.
VP8 also supports a mode where the encoding of a bitstream guarantees
all reconstructed pixel values between 0 and 255; compliant
bitstreams of such requirements have the clamp_type bit in the frame
header set to 1. In such a case, the clamp255 function is no longer
required.
The summation process is the same, regardless of the (intra or inter)
mode of prediction in effect for the macroblock. The reference
decoder implementation of reconstruction may be found in the file
idct_add.c.
Bankoski, et al. Informational [Page 83]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
15. Loop Filter
Loop filtering is the last stage of frame reconstruction and the
next-to-last stage of the decoding process. The loop filter is
applied to the entire frame after the summation of predictor and
residue signals, as described in Section 14.
The purpose of the loop filter is to eliminate (or at least reduce)
visually objectionable artifacts associated with the semi-
independence of the coding of macroblocks and their constituent
subblocks.
As was discussed in Section 5, the loop filter is "integral" to
decoding, in that the results of loop filtering are used in the
prediction of subsequent frames. Consequently, a functional decoder
implementation must perform loop filtering exactly as described here.
This is distinct from any postprocessing that may be applied only to
the image immediately before display; such postprocessing is entirely
at the option of the implementor (and/or user) and has no effect on
decoding per se.
The baseline frame-level parameters controlling the loop filter are
defined in the frame header (Section 9.4) along with a mechanism for
adjustment based on a macroblock's prediction mode and/or reference
frame. The first is a flag (filter_type) selecting the type of
filter (normal or simple); the other two are numbers
(loop_filter_level and sharpness_level) that adjust the strength or
sensitivity of the filter. As described in Sections 9.3 and 10,
loop_filter_level may also be overridden on a per-macroblock basis
using segmentation.
Loop filtering is one of the more computationally intensive aspects
of VP8 decoding. This is the reason for the existence of the
optional, less-demanding simple filter type.
Note carefully that loop filtering must be skipped entirely if
loop_filter_level at either the frame header level or macroblock
override level is 0. In no case should the loop filter be run with a
value of 0; it should instead be skipped.
We begin by discussing the aspects of loop filtering that are
independent of the controlling parameters and type of filter chosen.
Bankoski, et al. Informational [Page 84]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
15.1. Filter Geometry and Overall Procedure
The Y, U, and V planes are processed independently and identically.
The loop filter acts on the edges between adjacent macroblocks and on
the edges between adjacent subblocks of a macroblock. All such edges
are horizontal or vertical. For each pixel position on an edge, a
small number (two or three) of pixels adjacent to either side of the
position are examined and possibly modified. The displacements of
these pixels are at a right angle to the edge orientation; that is,
for a horizontal edge, we treat the pixels immediately above and
below the edge position, and for a vertical edge, we treat the pixels
immediately to the left and right of the edge.
We call this collection of pixels associated to an edge position a
segment; the length of a segment is 2, 4, 6, or 8. Excepting that
the normal filter uses slightly different algorithms for, and either
filter may apply different control parameters to, the edges between
macroblocks and those between subblocks, the treatment of edges is
quite uniform: All segments straddling an edge are treated
identically; there is no distinction between the treatment of
horizontal and vertical edges, whether between macroblocks or between
subblocks.
As a consequence, adjacent subblock edges within a macroblock may be
concatenated and processed in their entirety. There is a single
8-pixel-long vertical edge horizontally centered in each of the U and
V blocks (the concatenation of upper and lower 4-pixel edges between
chroma subblocks), and three 16-pixel-long vertical edges at
horizontal positions 1/4, 1/2, and 3/4 the width of the luma
macroblock, each representing the concatenation of four 4-pixel
sub-edges between pairs of Y subblocks.
The macroblocks comprising the frame are processed in the usual
raster-scan order. Each macroblock is "responsible for" the
inter-macroblock edges immediately above and to the left of it (but
not the edges below and to the right of it), as well as the edges
between its subblocks.
For each macroblock M, there are four filtering steps, which are,
(almost) in order:
1. If M is not on the leftmost column of macroblocks, filter across
the left (vertical) inter-macroblock edge of M.
2. Filter across the vertical subblock edges within M.
Bankoski, et al. Informational [Page 85]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
3. If M is not on the topmost row of macroblocks, filter across the
top (horizontal) inter-macroblock edge of M.
4. Filter across the horizontal subblock edges within M.
We write MY, MU, and MV for the planar constituents of M, that is,
the 16x16 luma block, 8x8 U block, and 8x8 V block comprising M.
In step 1, for each of the three blocks MY, MU, and MV, we filter
each of the (16 luma or 8 chroma) segments straddling the column
separating the block from the block immediately to the left of it,
using the inter-macroblock filter and controls associated to the
loop_filter_level and sharpness_level.
In step 4, we filter across the (three luma and one each for U and V)
vertical subblock edges described above, this time using the
inter-subblock filter and controls.
Steps 2 and 4 are skipped for macroblocks that satisfy both of the
following two conditions:
1. Macroblock coding mode is neither B_PRED nor SPLITMV; and
2. There is no DCT coefficient coded for the whole macroblock.
For these macroblocks, loop filtering for edges between subblocks
internal to a macroblock is effectively skipped. This skip strategy
significantly reduces VP8 loop-filtering complexity.
Edges between macroblocks and those between subblocks are treated
with different control parameters (and, in the case of the normal
filter, with different algorithms). Except for pixel addressing,
there is no distinction between the treatment of vertical and
horizontal edges. Luma edges are always 16 pixels long, chroma edges
are always 8 pixels long, and the segments straddling an edge are
treated identically; this of course facilitates vector processing.
Because many pixels belong to segments straddling two or more edges,
and so will be filtered more than once, the order in which edges are
processed given above must be respected by any implementation.
Within a single edge, however, the segments straddling that edge are
disjoint, and the order in which these segments are processed is
immaterial.
Before taking up the filtering algorithms themselves, we should
emphasize a point already made: Even though the pixel segments
associated to a macroblock are antecedent to the macroblock (that is,
lie within the macroblock or in already-constructed macroblocks), a
Bankoski, et al. Informational [Page 86]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
macroblock must not be filtered immediately after its
"reconstruction" (described in Section 14). Rather, the loop filter
applies after all the macroblocks have been "reconstructed" (i.e.,
had their predictor summed with their residue); correct decoding is
predicated on the fact that already-constructed portions of the
current frame referenced via intra-prediction (described in
Section 12) are not yet filtered.
15.2. Simple Filter
Having described the overall procedure of, and pixels affected by,
the loop filter, we turn our attention to the treatment of individual
segments straddling edges. We begin by describing the simple filter,
which, as the reader might guess, is somewhat simpler than the normal
filter.
Note that the simple filter only applies to luma edges. Chroma edges
are left unfiltered.
Roughly speaking, the idea of loop filtering is, within limits, to
reduce the difference between pixels straddling an edge. Differences
in excess of a threshold (associated to the loop_filter_level) are
assumed to be "natural" and are unmodified; differences below the
threshold are assumed to be artifacts of quantization and the
(partially) separate coding of blocks, and are reduced via the
procedures described below. While the loop_filter_level is in
principle arbitrary, the levels chosen by a VP8 compressor tend to be
correlated to quantizer levels.
Most of the filtering arithmetic is done using 8-bit signed operands
(having a range of -128 to +127, inclusive), supplemented by 16-bit
temporaries holding results of multiplies.
Sums and other temporaries need to be "clamped" to a valid signed
8-bit range:
---- Begin code block --------------------------------------
int8 c(int v)
{
return (int8) (v < -128 ? -128 : (v < 128 ? v : 127));
}
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 87]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
Since pixel values themselves are unsigned 8-bit numbers, we need to
convert between signed and unsigned values:
---- Begin code block --------------------------------------
/* Convert pixel value (0 <= v <= 255) to an 8-bit signed
number. */
int8 u2s(Pixel v) { return (int8) (v - 128);}
/* Clamp, then convert signed number back to pixel value. */
Pixel s2u(int v) { return (Pixel) (c(v) + 128);}
---- End code block ----------------------------------------
Filtering is often predicated on absolute-value thresholds. The
following function is the equivalent of the standard library function
abs, whose prototype is found in the standard header file stdlib.h.
For us, the argument v is always the difference between two pixels
and lies in the range -255 <= v <= +255.
---- Begin code block --------------------------------------
int abs(int v) { return v < 0? -v : v;}
---- End code block ----------------------------------------
An actual implementation would of course use inline functions or
macros to accomplish these trivial procedures (which are used by both
the normal and simple loop filters). An optimal implementation would
probably express them in machine language, perhaps using single
instruction, multiple data (SIMD) vector instructions. On many SIMD
processors, the saturation accomplished by the above clamping
function is often folded into the arithmetic instructions themselves,
obviating the explicit step taken here.
To simplify the specification of relative pixel positions, we use the
word "before" to mean "immediately above" (for a vertical segment
straddling a horizontal edge) or "immediately to the left of" (for a
horizontal segment straddling a vertical edge), and the word "after"
to mean "immediately below" or "immediately to the right of".
Given an edge, a segment, and a limit value, the simple loop filter
computes a value based on the four pixels that straddle the edge (two
either side). If that value is below a supplied limit, then, very
roughly speaking, the two pixel values are brought closer to each
other, "shaving off" something like a quarter of the difference. The
Bankoski, et al. Informational [Page 88]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
same procedure is used for all segments straddling any type of edge,
regardless of the nature (inter-macroblock, inter-subblock, luma, or
chroma) of the edge; only the limit value depends on the edge type.
The exact procedure (for a single segment) is as follows; the
subroutine common_adjust is used by both the simple filter presented
here and the normal filters discussed in Section 15.3.
---- Begin code block --------------------------------------
int8 common_adjust(
int use_outer_taps, /* filter is 2 or 4 taps wide */
const Pixel *P1, /* pixel before P0 */
Pixel *P0, /* pixel before edge */
Pixel *Q0, /* pixel after edge */
const Pixel *Q1 /* pixel after Q0 */
) {
cint8 p1 = u2s(*P1); /* retrieve and convert all 4 pixels */
cint8 p0 = u2s(*P0);
cint8 q0 = u2s(*Q0);
cint8 q1 = u2s(*Q1);
/* Disregarding clamping, when "use_outer_taps" is false,
"a" is 3*(q0-p0). Since we are about to divide "a" by
8, in this case we end up multiplying the edge
difference by 5/8.
When "use_outer_taps" is true (as for the simple filter),
"a" is p1 - 3*p0 + 3*q0 - q1, which can be thought of as
a refinement of 2*(q0 - p0), and the adjustment is
something like (q0 - p0)/4. */
int8 a = c((use_outer_taps? c(p1 - q1) : 0) + 3*(q0 - p0));
/* b is used to balance the rounding of a/8 in the case where
the "fractional" part "f" of a/8 is exactly 1/2. */
cint8 b = (c(a + 3)) >> 3;
/* Divide a by 8, rounding up when f >= 1/2.
Although not strictly part of the C language,
the right shift is assumed to propagate the sign bit. */
a = c(a + 4) >> 3;
/* Subtract "a" from q0, "bringing it closer" to p0. */
*Q0 = s2u(q0 - a);
Bankoski, et al. Informational [Page 89]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/* Add "a" (with adjustment "b") to p0, "bringing it closer"
to q0.
The clamp of "a+b", while present in the reference decoder,
is superfluous; we have -16 <= a <= 15 at this point. */
*P0 = s2u(p0 + b);
return a;
}
---- End code block ----------------------------------------
---- Begin code block --------------------------------------
void simple_segment(
uint8 edge_limit, /* do nothing if edge difference
exceeds limit */
const Pixel *P1, /* pixel before P0 */
Pixel *P0, /* pixel before edge */
Pixel *Q0, /* pixel after edge */
const Pixel *Q1 /* pixel after Q0 */
) {
if ((abs(*P0 - *Q0)*2 + abs(*P1 - *Q1)/2) <= edge_limit))
common_adjust(1, P1, P0, Q0, Q1); /* use outer taps */
}
---- End code block ----------------------------------------
We make a couple of remarks about the rounding procedure above. When
b is zero (that is, when the "fractional part" of a is not 1/2), we
are (except for clamping) adding the same number to p0 as we are
subtracting from q0. This preserves the average value of p0 and q0,
but the resulting difference between p0 and q0 is always even; in
particular, the smallest non-zero gradation +-1 is not possible here.
When b is one, the value we add to p0 (again except for clamping) is
one less than the value we are subtracting from q0. In this case,
the resulting difference is always odd (and the small gradation +-1
is possible), but the average value is reduced by 1/2, yielding, for
instance, a very slight darkening in the luma plane. (In the very
unlikely event of appreciable darkening after a large number of
interframes, a compressor would of course eventually compensate for
this in the selection of predictor and/or residue.)
Bankoski, et al. Informational [Page 90]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
The derivation of the edge_limit value used above, which depends on
the loop_filter_level and sharpness_level, as well as the type of
edge being processed, will be taken up after we describe the normal
loop filtering algorithm below.
15.3. Normal Filter
The normal loop filter is a refinement of the simple loop filter; all
of the general discussion above applies here as well. In particular,
the functions c, u2s, s2u, abs, and common_adjust are used by both
the normal and simple filters.
As mentioned above, the normal algorithms for inter-macroblock and
inter-subblock edges differ. Nonetheless, they have a great deal in
common: They use similar threshold algorithms to disable the filter
and to detect high internal edge variance (which influences the
filtering algorithm). Both algorithms also use, at least
conditionally, the simple filter adjustment procedure described
above.
The common thresholding algorithms are as follows.
---- Begin code block --------------------------------------
/* All functions take (among other things) a segment (of length
at most 4 + 4 = 8) symmetrically straddling an edge.
The pixel values (or pointers) are always given in order,
from the "beforemost" to the "aftermost". So, for a
horizontal edge (written "|"), an 8-pixel segment would be
ordered p3 p2 p1 p0 | q0 q1 q2 q3. */
/* Filtering is disabled if the difference between any two
adjacent "interior" pixels in the 8-pixel segment exceeds
the relevant threshold (I). A more complex thresholding
calculation is done for the group of four pixels that
straddle the edge, in line with the calculation in
simple_segment() above. */
Bankoski, et al. Informational [Page 91]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
int filter_yes(
uint8 I, /* limit on interior differences */
uint8 E, /* limit at the edge */
cint8 p3, cint8 p2, cint8 p1, cint8 p0, /* pixels before
edge */
cint8 q0, cint8 q1, cint8 q2, cint8 q3 /* pixels after
edge */
) {
return (abs(p0 - q0)*2 + abs(p1 - q1)/2) <= E
&& abs(p3 - p2) <= I && abs(p2 - p1) <= I &&
abs(p1 - p0) <= I
&& abs(q3 - q2) <= I && abs(q2 - q1) <= I &&
abs(q1 - q0) <= I;
}
---- End code block ----------------------------------------
---- Begin code block --------------------------------------
/* Filtering is altered if (at least) one of the differences
on either side of the edge exceeds a threshold (we have
"high edge variance"). */
int hev(
uint8 threshold,
cint8 p1, cint8 p0, /* pixels before edge */
cint8 q0, cint8 q1 /* pixels after edge */
) {
return abs(p1 - p0) > threshold || abs(q1 - q0) > threshold;
}
---- End code block ----------------------------------------
The subblock filter is a variant of the simple filter. In fact, if
we have high edge variance, the adjustment is exactly as for the
simple filter. Otherwise, the simple adjustment (without outer taps)
is applied, and the two pixels one step in from the edge pixels are
adjusted by roughly half the amount by which the two edge pixels are
adjusted; since the edge adjustment here is essentially 3/8 the edge
difference, the inner adjustment is approximately 3/16 the edge
difference.
Bankoski, et al. Informational [Page 92]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
---- Begin code block --------------------------------------
void subblock_filter(
uint8 hev_threshold, /* detect high edge variance */
uint8 interior_limit, /* possibly disable filter */
uint8 edge_limit,
cint8 *P3, cint8 *P2, int8 *P1, int8 *P0, /* pixels before
edge */
int8 *Q0, int8 *Q1, cint8 *Q2, cint8 *Q3 /* pixels after
edge */
) {
cint8 p3 = u2s(*P3), p2 = u2s(*P2), p1 = u2s(*P1),
p0 = u2s(*P0);
cint8 q0 = u2s(*Q0), q1 = u2s(*Q1), q2 = u2s(*Q2),
q3 = u2s(*Q3);
if (filter_yes(interior_limit, edge_limit, q3, q2, q1, q0,
p0, p1, p2, p3))
{
const int hv = hev(hev_threshold, p1, p0, q0, q1);
cint8 a = (common_adjust(hv, P1, P0, Q0, Q1) + 1) >> 1;
if (!hv) {
*Q1 = s2u(q1 - a);
*P1 = s2u(p1 + a);
}
}
}
---- End code block ----------------------------------------
The inter-macroblock filter has potentially wider scope. If the edge
variance is high, it performs the simple adjustment (using the outer
taps, just like the simple filter and the corresponding case of the
normal subblock filter). If the edge variance is low, we begin with
the same basic filter calculation and apply multiples of it to pixel
pairs symmetric about the edge; the magnitude of adjustment decays as
we move away from the edge and six of the pixels in the segment are
affected.
Bankoski, et al. Informational [Page 93]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
---- Begin code block --------------------------------------
void MBfilter(
uint8 hev_threshold, /* detect high edge variance */
uint8 interior_limit, /* possibly disable filter */
uint8 edge_limit,
cint8 *P3, int8 *P2, int8 *P1, int8 *P0, /* pixels before
edge */
int8 *Q0, int8 *Q1, int8 *Q2, cint8 *Q3 /* pixels after
edge */
) {
cint8 p3 = u2s(*P3), p2 = u2s(*P2), p1 = u2s(*P1),
p0 = u2s(*P0);
cint8 q0 = u2s(*Q0), q1 = u2s(*Q1), q2 = u2s(*Q2),
q3 = u2s(*Q3);
if (filter_yes(interior_limit, edge_limit, q3, q2, q1, q0,
p0, p1, p2, p3))
{
if (!hev(hev_threshold, p1, p0, q0, q1))
{
/* Same as the initial calculation in "common_adjust",
w is something like twice the edge difference */
const int8 w = c(c(p1 - q1) + 3*(q0 - p0));
/* 9/64 is approximately 9/63 = 1/7, and 1<<7 = 128 =
2*64. So this a, used to adjust the pixels adjacent
to the edge, is something like 3/7 the edge
difference. */
int8 a = c((27*w + 63) >> 7);
*Q0 = s2u(q0 - a); *P0 = s2u(p0 + a);
/* Next two are adjusted by 2/7 the edge difference */
a = c((18*w + 63) >> 7);
*Q1 = s2u(q1 - a); *P1 = s2u(p1 + a);
/* Last two are adjusted by 1/7 the edge difference */
a = c((9*w + 63) >> 7);
*Q2 = s2u(q2 - a); *P2 = s2u(p2 + a);
Bankoski, et al. Informational [Page 94]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
} else /* if hev, do simple filter */
common_adjust(1, P1, P0, Q0, Q1); /* using outer
taps */
}
}
---- End code block ----------------------------------------
15.4. Calculation of Control Parameters
We conclude the discussion of loop filtering by showing how the
thresholds supplied to the procedures above are derived from the two
control parameters sharpness_level (an unsigned 3-bit number having
maximum value 7) and loop_filter_level (an unsigned 6-bit number
having maximum value 63).
While the sharpness_level is constant over the frame, individual
macroblocks may override the loop_filter_level with one of four
possibilities supplied in the frame header (as described in
Section 10).
Both the simple and normal filters disable filtering if a value
derived from the four pixels that straddle the edge (2 either side)
exceeds a threshold / limit value.
---- Begin code block --------------------------------------
/* Luma and Chroma use the same inter-macroblock edge limit */
uint8 mbedge_limit = ((loop_filter_level + 2) * 2) +
interior_limit;
/* Luma and Chroma use the same inter-subblock edge limit */
uint8 sub_bedge_limit = (loop_filter_level * 2) + interior_limit;
---- End code block ----------------------------------------
The remaining thresholds are used only by the normal filters. The
filter-disabling interior difference limit is the same for all edges
(luma, chroma, inter-subblock, inter-macroblock) and is given by the
following.
Bankoski, et al. Informational [Page 95]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
---- Begin code block --------------------------------------
uint8 interior_limit = loop_filter_level;
if (sharpness_level)
{
interior_limit >>= sharpness_level > 4 ? 2 : 1;
if (interior_limit > 9 - sharpness_level)
interior_limit = 9 - sharpness_level;
}
if (!interior_limit)
interior_limit = 1;
---- End code block ----------------------------------------
Finally, we give the derivation of the high edge-variance threshold,
which is also the same for all edge types.
---- Begin code block --------------------------------------
uint8 hev_threshold = 0;
if (we_are_decoding_akey_frame) /* current frame is a key frame */
{
if (loop_filter_level >= 40)
hev_threshold = 2;
else if (loop_filter_level >= 15)
hev_threshold = 1;
}
else /* current frame is an interframe */
{
if (loop_filter_level >= 40)
hev_threshold = 3;
else if (loop_filter_level >= 20)
hev_threshold = 2;
else if (loop_filter_level >= 15)
hev_threshold = 1;
}
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 96]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
16. Interframe Macroblock Prediction Records
We describe the layout and semantics of the prediction records for
macroblocks in an interframe.
After the feature specification (which is described in Section 10 and
is identical for intraframes and interframes), there comes a
Bool(prob_intra), which indicates inter-prediction (i.e., prediction
from prior frames) when true and intra-prediction (i.e., prediction
from already-coded portions of the current frame) when false. The
zero-probability prob_intra is set by field J of the frame header.
16.1. Intra-Predicted Macroblocks
For intra-prediction, the layout of the prediction data is
essentially the same as the layout for key frames, although the
contexts used by the decoding process are slightly different.
As discussed in Section 8, the "outer" Y mode here uses a different
tree from that used in key frames, repeated here for convenience.
---- Begin code block --------------------------------------
const tree_index ymode_tree [2 * (num_ymodes - 1)] =
{
-DC_PRED, 2, /* root: DC_PRED = "0", "1" subtree */
4, 6, /* "1" subtree has 2 descendant subtrees */
-V_PRED, -H_PRED, /* "10" subtree: V_PRED = "100",
H_PRED = "101" */
-TM_PRED, -B_PRED /* "11" subtree: TM_PRED = "110",
B_PRED = "111" */
};
---- End code block ----------------------------------------
The probability table used to decode this tree is variable. As
described in Section 11, it (along with the similarly treated UV
table) can be updated by field J of the frame header. Similar to the
coefficient-decoding probabilities, such updates are cumulative and
affect all ensuing frames until the next key frame or explicit
update. The default probabilities for the Y and UV tables are:
---- Begin code block --------------------------------------
Prob ymode_prob [num_ymodes - 1] = { 112, 86, 140, 37};
Prob uv_mode_prob [num_uv_modes - 1] = { 162, 101, 204};
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 97]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
These defaults must be restored after detection of a key frame.
Just as for key frames, if the Y mode is B_PRED, there next comes an
encoding of the intra_bpred mode used by each of the sixteen Y
subblocks. These encodings use the same tree as does that for key
frames but, in place of the contexts used in key frames, these
encodings use the single fixed probability table.
---- Begin code block --------------------------------------
const Prob bmode_prob [num_intra_bmodes - 1] = {
120, 90, 79, 133, 87, 85, 80, 111, 151
};
---- End code block ----------------------------------------
Last comes the chroma mode, again coded using the same tree as that
used for key frames, this time using the dynamic uv_mode_prob table
described above.
The calculation of the intra-prediction buffer is identical to that
described for key frames in Section 12.
16.2. Inter-Predicted Macroblocks
Otherwise (when the above bool is true), we are using
inter-prediction (which of course only happens for interframes), to
which we now restrict our attention.
The next datum is then another bool, B(prob_last), selecting the
reference frame. If 0, the reference frame is the previous frame
(the last frame); if 1, another bool (prob_gf) selects the reference
frame between the golden frame (0) and the altref frame (1). The
probabilities prob_last and prob_gf are set in field J of the frame
header.
Together with setting the reference frame, the purpose of inter-mode
decoding is to set a motion vector for each of the sixteen Y
subblocks of the current macroblock. These settings then define the
calculation of the inter-prediction buffer (detailed in Section 18).
While the net effect of inter-mode decoding is straightforward, the
implementation is somewhat complex; the (lossless) compression
achieved by this method justifies the complexity.
Bankoski, et al. Informational [Page 98]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
After the reference frame selector comes the mode (or motion vector
reference) applied to the macroblock as a whole, coded using the
following enumeration and tree. Setting mv_nearest = num_ymodes is a
convenience that allows a single variable to unambiguously hold an
inter- or intra-prediction mode.
---- Begin code block --------------------------------------
typedef enum
{
mv_nearest = num_ymodes, /* use "nearest" motion vector
for entire MB */
mv_near, /* use "next nearest" "" */
mv_zero, /* use zero "" */
mv_new, /* use explicit offset from
implicit "" */
mv_split, /* use multiple motion vectors */
num_mv_refs = mv_split + 1 - mv_nearest
}
mv_ref;
const tree_index mv_ref_tree [2 * (num_mv_refs - 1)] =
{
-mv_zero, 2, /* zero = "0" */
-mv_nearest, 4, /* nearest = "10" */
-mv_near, 6, /* near = "110" */
-mv_new, -mv_split /* new = "1110", split = "1111" */
};
---- End code block ----------------------------------------
16.3. Mode and Motion Vector Contexts
The probability table used to decode the mv_ref, along with three
reference motion vectors used by the selected mode, is calculated via
a survey of the already-decoded motion vectors in (up to) 3 nearby
macroblocks.
The algorithm generates a sorted list of distinct motion vectors
adjacent to the search site. The best_mv is the vector with the
highest score. The mv_nearest is the non-zero vector with the
highest score. The mv_near is the non-zero vector with the next
highest score. The number of motion vectors coded using the SPLITMV
mode is scored using the same weighting and is returned with the
scores of the best, nearest, and near vectors.
Bankoski, et al. Informational [Page 99]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
The three adjacent macroblocks above, left, and above-left are
considered in order. If the macroblock is intra-coded, no action is
taken. Otherwise, the motion vector is compared to other previously
found motion vectors to determine if it has been seen before, and if
so contributes its weight to that vector; otherwise, it enters a new
vector in the list. The above and left vectors have twice the weight
of the above-left vector.
As is the case with many contexts used by VP8, it is possible for
macroblocks near the top or left edges of the image to reference
blocks that are outside the visible image. VP8 provides a border of
1 macroblock filled with 0x0 motion vectors left of the left edge,
and a border filled with 0,0 motion vectors of 1 macroblocks above
the top edge.
Much of the process is more easily described in C than in English.
The reference code for this can be found in modemv.c (Section 20.11).
The calculation of reference vectors, probability table, and,
finally, the inter-prediction mode itself is implemented as follows.
---- Begin code block --------------------------------------
typedef union
{
unsigned int as_int;
MV as_mv;
} int_mv; /* facilitates rapid equality tests */
static void mv_bias(MODE_INFO *x,int refframe, int_mv *mvp,
int * ref_frame_sign_bias)
{
MV xmv;
xmv = x->mbmi.mv.as_mv;
if ( ref_frame_sign_bias[x->mbmi.ref_frame] !=
ref_frame_sign_bias[refframe] )
{
xmv.row*=-1;
xmv.col*=-1;
}
mvp->as_mv = xmv;
}
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 100]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
---- Begin code block --------------------------------------
void vp8_clamp_mv(MV *mv, const MACROBLOCKD *xd)
{
if ( mv->col < (xd->mb_to_left_edge - LEFT_TOP_MARGIN) )
mv->col = xd->mb_to_left_edge - LEFT_TOP_MARGIN;
else if ( mv->col > xd->mb_to_right_edge + RIGHT_BOTTOM_MARGIN )
mv->col = xd->mb_to_right_edge + RIGHT_BOTTOM_MARGIN;
if ( mv->row < (xd->mb_to_top_edge - LEFT_TOP_MARGIN) )
mv->row = xd->mb_to_top_edge - LEFT_TOP_MARGIN;
else if ( mv->row > xd->mb_to_bottom_edge + RIGHT_BOTTOM_MARGIN )
mv->row = xd->mb_to_bottom_edge + RIGHT_BOTTOM_MARGIN;
}
---- End code block ----------------------------------------
In the function vp8_find_near_mvs(), the vectors "nearest" and "near"
are used by the corresponding modes.
The vector best_mv is used as a base for explicitly coded motion
vectors.
The first three entries in the return value cnt are (in order)
weighted census values for "zero", "nearest", and "near" vectors.
The final value indicates the extent to which SPLITMV was used by the
neighboring macroblocks. The largest possible "weight" value in each
case is 5.
---- Begin code block --------------------------------------
void vp8_find_near_mvs
(
MACROBLOCKD *xd,
const MODE_INFO *here,
MV *nearest,
MV *near,
MV *best_mv,
int cnt[4],
int refframe,
int * ref_frame_sign_bias
)
Bankoski, et al. Informational [Page 101]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{
const MODE_INFO *above = here - xd->mode_info_stride;
const MODE_INFO *left = here - 1;
const MODE_INFO *aboveleft = above - 1;
int_mv near_mvs[4];
int_mv *mv = near_mvs;
int *cntx = cnt;
enum {CNT_ZERO, CNT_NEAREST, CNT_NEAR, CNT_SPLITMV};
/* Zero accumulators */
mv[0].as_int = mv[1].as_int = mv[2].as_int = 0;
cnt[0] = cnt[1] = cnt[2] = cnt[3] = 0;
/* Process above */
if (above->mbmi.ref_frame != INTRA_FRAME) {
if (above->mbmi.mv.as_int) {
(++mv)->as_int = above->mbmi.mv.as_int;
mv_bias(above, refframe, mv, ref_frame_sign_bias);
++cntx;
}
*cntx += 2;
}
/* Process left */
if (left->mbmi.ref_frame != INTRA_FRAME) {
if (left->mbmi.mv.as_int) {
int_mv this_mv;
this_mv.as_int = left->mbmi.mv.as_int;
mv_bias(left, refframe, &this_mv, ref_frame_sign_bias);
if (this_mv.as_int != mv->as_int) {
(++mv)->as_int = this_mv.as_int;
++cntx;
}
*cntx += 2;
} else
cnt[CNT_ZERO] += 2;
}
/* Process above left */
if (aboveleft->mbmi.ref_frame != INTRA_FRAME) {
if (aboveleft->mbmi.mv.as_int) {
int_mv this_mv;
this_mv.as_int = aboveleft->mbmi.mv.as_int;
mv_bias(aboveleft, refframe, &this_mv,
ref_frame_sign_bias);
Bankoski, et al. Informational [Page 102]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
if (this_mv.as_int != mv->as_int) {
(++mv)->as_int = this_mv.as_int;
++cntx;
}
*cntx += 1;
} else
cnt[CNT_ZERO] += 1;
}
/* If we have three distinct MVs ... */
if (cnt[CNT_SPLITMV]) {
/* See if above-left MV can be merged with NEAREST */
if (mv->as_int == near_mvs[CNT_NEAREST].as_int)
cnt[CNT_NEAREST] += 1;
}
cnt[CNT_SPLITMV] = ((above->mbmi.mode == SPLITMV)
+ (left->mbmi.mode == SPLITMV)) * 2
+ (aboveleft->mbmi.mode == SPLITMV);
/* Swap near and nearest if necessary */
if (cnt[CNT_NEAR] > cnt[CNT_NEAREST]) {
int tmp;
tmp = cnt[CNT_NEAREST];
cnt[CNT_NEAREST] = cnt[CNT_NEAR];
cnt[CNT_NEAR] = tmp;
tmp = near_mvs[CNT_NEAREST].as_int;
near_mvs[CNT_NEAREST].as_int = near_mvs[CNT_NEAR].as_int;
near_mvs[CNT_NEAR].as_int = tmp;
}
/* Use near_mvs[0] to store the "best" MV */
if (cnt[CNT_NEAREST] >= cnt[CNT_ZERO])
near_mvs[CNT_ZERO] = near_mvs[CNT_NEAREST];
/* Set up return values */
*best_mv = near_mvs[0].as_mv;
*nearest = near_mvs[CNT_NEAREST].as_mv;
*near = near_mvs[CNT_NEAR].as_mv;
vp8_clamp_mv(nearest, xd);
vp8_clamp_mv(near, xd);
vp8_clamp_mv(best_mv, xd); //TODO: Move this up before
the copy
}
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 103]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
The mv_ref probability table (mv_ref_p) is then derived from the
census as follows.
---- Begin code block --------------------------------------
const int vp8_mode_contexts[6][4] =
{
{ 7, 1, 1, 143, },
{ 14, 18, 14, 107, },
{ 135, 64, 57, 68, },
{ 60, 56, 128, 65, },
{ 159, 134, 128, 34, },
{ 234, 188, 128, 28, },
}
---- End code block ----------------------------------------
---- Begin code block --------------------------------------
vp8_prob *vp8_mv_ref_probs(vp8_prob mv_ref_p[VP8_MVREFS-1],
int cnt[4])
{
mv_ref_p[0] = vp8_mode_contexts [cnt[0]] [0];
mv_ref_p[1] = vp8_mode_contexts [cnt[1]] [1];
mv_ref_p[2] = vp8_mode_contexts [cnt[2]] [2];
mv_ref_p[3] = vp8_mode_contexts [cnt[3]] [3];
return p;
}
---- End code block ----------------------------------------
Once mv_ref_p is established, the mv_ref is decoded as usual.
---- Begin code block --------------------------------------
mvr = (mv_ref) treed_read(d, mv_ref_tree, mv_ref_p);
---- End code block ----------------------------------------
For the first four inter-coding modes, the same motion vector is used
for all the Y subblocks. The first three modes use an implicit
motion vector.
Bankoski, et al. Informational [Page 104]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
+------------+------------------------------------------------------+
| Mode | Instruction |
+------------+------------------------------------------------------+
| mv_nearest | Use the nearest vector returned by |
| | vp8_find_near_mvs. |
| | |
| mv_near | Use the near vector returned by vp8_find_near_mvs. |
| | |
| mv_zero | Use a zero vector; that is, predict the current |
| | macroblock from the corresponding macroblock in the |
| | prediction frame. |
| | |
| NEWMV | This mode is followed by an explicitly coded motion |
| | vector (the format of which is described in the next |
| | section) that is added (component-wise) to the |
| | best_mv reference vector returned by find_near_mvs |
| | and applied to all 16 subblocks. |
+------------+------------------------------------------------------+
16.4. Split Prediction
The remaining mode (SPLITMV) causes multiple vectors to be applied to
the Y subblocks. It is immediately followed by a partition
specification that determines how many vectors will be specified and
how they will be assigned to the subblocks. The possible partitions,
with indicated subdivisions and coding tree, are as follows.
---- Begin code block --------------------------------------
typedef enum
{
mv_top_bottom, /* two pieces {0...7} and {8...15} */
mv_left_right, /* {0,1,4,5,8,9,12,13} and
{2,3,6,7,10,11,14,15} */
mv_quarters, /* {0,1,4,5}, {2,3,6,7}, {8,9,12,13},
{10,11,14,15} */
MV_16, /* every subblock gets its own vector
{0} ... {15} */
mv_num_partitions
}
MVpartition;
Bankoski, et al. Informational [Page 105]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
const tree_index mvpartition_tree [2 * (mvnum_partition - 1)] =
{
-MV_16, 2, /* MV_16 = "0" */
-mv_quarters, 4, /* mv_quarters = "10" */
-mv_top_bottom, -mv_left_right /* top_bottom = "110",
left_right = "111" */
};
---- End code block ----------------------------------------
The partition is decoded using a fixed, constant probability table:
---- Begin code block --------------------------------------
const Prob mvpartition_probs [mvnum_partition - 1] =
{ 110, 111, 150};
part = (MVpartition) treed_read(d, mvpartition_tree,
mvpartition_probs);
---- End code block ----------------------------------------
After the partition come two (for mv_top_bottom or mv_left_right),
four (for mv_quarters), or sixteen (for MV_16) subblock
inter-prediction modes. These modes occur in the order indicated by
the partition layouts (given as comments to the MVpartition enum) and
are coded as follows. (As was done for the macroblock-level modes,
we offset the mode enumeration so that a single variable may
unambiguously hold either an intra- or inter-subblock mode.)
Prior to decoding each subblock, a decoding tree context is chosen as
illustrated in the code snippet below. The context is based on the
immediate left and above subblock neighbors, and whether they are
equal, are zero, or a combination of those.
---- Begin code block --------------------------------------
typedef enum
{
LEFT4x4 = num_intra_bmodes, /* use already-coded MV to
my left */
ABOVE4x4, /* use already-coded MV above me */
ZERO4x4, /* use zero MV */
NEW4x4, /* explicit offset from "best" */
num_sub_mv_ref
};
sub_mv_ref;
Bankoski, et al. Informational [Page 106]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
const tree_index sub_mv_ref_tree [2 * (num_sub_mv_ref - 1)] =
{
-LEFT4X4, 2, /* LEFT = "0" */
-ABOVE4X4, 4, /* ABOVE = "10" */
-ZERO4X4, -NEW4X4 /* ZERO = "110", NEW = "111" */
};
/* Choose correct decoding tree context
* Function parameters are left subblock neighbor MV and above
* subblock neighbor MV */
int vp8_mvCont(MV *l, MV*a)
{
int lez = (l->row == 0 && l->col == 0); /* left neighbor
is zero */
int aez = (a->row == 0 && a->col == 0); /* above neighbor
is zero */
int lea = (l->row == a->row && l->col == a->col); /* left
neighbor equals above neighbor */
if (lea && lez)
return SUBMVREF_LEFT_ABOVE_ZED; /* =4 */
if (lea)
return SUBMVREF_LEFT_ABOVE_SAME; /* =3 */
if (aez)
return SUBMVREF_ABOVE_ZED; /* =2 */
if (lez)
return SUBMVREF_LEFT_ZED; /* =1*/
return SUBMVREF_NORMAL; /* =0 */
}
/* Constant probabilities and decoding procedure. */
const Prob sub_mv_ref_prob [5][num_sub_mv_ref - 1] = {
{ 147,136,18 },
{ 106,145,1 },
{ 179,121,1 },
{ 223,1 ,34 },
{ 208,1 ,1 }
};
sub_ref = (sub_mv_ref) treed_read(d, sub_mv_ref_tree,
sub_mv_ref_prob[context]);
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 107]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
The first two sub-prediction modes simply copy the already-coded
motion vectors used by the blocks above and to the left of the
subblock at the upper left corner of the current subset (i.e.,
collection of subblocks being predicted). These prediction blocks
need not lie in the current macroblock and, if the current subset
lies at the top or left edges of the frame, need not lie in the
frame. In this latter case, their motion vectors are taken to be
zero, as are subblock motion vectors within an intra-predicted
macroblock. Also, to ensure the correctness of prediction within
this macroblock, all subblocks lying in an already-decoded subset of
the current macroblock must have their motion vectors set.
ZERO4x4 uses a zero motion vector and predicts the current subset
using the corresponding subset from the prediction frame.
NEW4x4 is exactly like NEWMV except that NEW4x4 is applied only to
the current subset. It is followed by a two-dimensional motion
vector offset (described in the next section) that is added to the
best vector returned by the earlier call to find_near_mvs to form the
motion vector in effect for the subset.
Parsing of both inter-prediction modes and motion vectors (described
next) can be found in the reference decoder file modemv.c
(Section 20.11).
17. Motion Vector Decoding
As discussed above, motion vectors appear in two places in the VP8
datastream: applied to whole macroblocks in NEWMV mode and applied to
subsets of macroblocks in NEW4x4 mode. The format of the vectors is
identical in both cases.
Each vector has two pieces: a vertical component (row) followed by a
horizontal component (column). The row and column use separate
coding probabilities but are otherwise represented identically.
17.1. Coding of Each Component
Each component is a signed integer V representing a vertical or
horizontal luma displacement of V quarter-pixels (and a chroma
displacement of V eighth-pixels). The absolute value of V, if
non-zero, is followed by a boolean sign. V may take any value
between -1023 and +1023, inclusive.
Bankoski, et al. Informational [Page 108]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
The absolute value A is coded in one of two different ways according
to its size. For 0 <= A <= 7, A is tree-coded, and for 8 <= A <=
1023, the bits in the binary expansion of A are coded using
independent boolean probabilities. The coding of A begins with a
bool specifying which range is in effect.
Decoding a motion vector component then requires a 19-position
probability table, whose offsets, along with the procedure used to
decode components, are as follows:
---- Begin code block --------------------------------------
typedef enum
{
mvpis_short, /* short (<= 7) vs long (>= 8) */
MVPsign, /* sign for non-zero */
MVPshort, /* 8 short values = 7-position tree */
MVPbits = MVPshort + 7, /* 8 long value bits
w/independent probs */
MVPcount = MVPbits + 10 /* 19 probabilities in total */
}
MVPindices;
typedef Prob MV_CONTEXT [MVPcount]; /* Decoding spec for
a single component */
/* Tree used for small absolute values (has expected
correspondence). */
const tree_index small_mvtree [2 * (8 - 1)] =
{
2, 8, /* "0" subtree, "1" subtree */
4, 6, /* "00" subtree, "01" subtree */
-0, -1, /* 0 = "000", 1 = "001" */
-2, -3, /* 2 = "010", 3 = "011" */
10, 12, /* "10" subtree, "11" subtree */
-4, -5, /* 4 = "100", 5 = "101" */
-6, -7 /* 6 = "110", 7 = "111" */
};
/* Read MV component at current decoder position, using
supplied probs. */
int read_mvcomponent(bool_decoder *d, const MV_CONTEXT *mvc)
{
const Prob * const p = (const Prob *) mvc;
Bankoski, et al. Informational [Page 109]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
int A = 0;
if (read_bool(d, p [mvpis_short])) /* 8 <= A <= 1023 */
{
/* Read bits 0, 1, 2 */
int i = 0;
do { A += read_bool(d, p [MVPbits + i]) << i;}
while (++i < 3);
/* Read bits 9, 8, 7, 6, 5, 4 */
i = 9;
do { A += read_bool(d, p [MVPbits + i]) << i;}
while (--i > 3);
/* We know that A >= 8 because it is coded long,
so if A <= 15, bit 3 is one and is not
explicitly coded. */
if (!(A & 0xfff0) || read_bool(d, p [MVPbits + 3]))
A += 8;
}
else /* 0 <= A <= 7 */
A = treed_read(d, small_mvtree, p + MVPshort);
return A && read_bool(r, p [MVPsign]) ? -A : A;
}
---- End code block ----------------------------------------
17.2. Probability Updates
The decoder should maintain an array of two MV_CONTEXTs for decoding
row and column components, respectively. These MV_CONTEXTs should be
set to their defaults every key frame. Each individual probability
may be updated every interframe (by field J of the frame header)
using a constant table of update probabilities. Each optional update
is of the form B? P(7), that is, a bool followed by a 7-bit
probability specification if true.
As with other dynamic probabilities used by VP8, the updates remain
in effect until the next key frame or until replaced via another
update.
Bankoski, et al. Informational [Page 110]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
In detail, the probabilities should then be managed as follows.
---- Begin code block --------------------------------------
/* Never-changing table of update probabilities for each
individual probability used in decoding motion vectors. */
const MV_CONTEXT vp8_mv_update_probs[2] =
{
{
237,
246,
253, 253, 254, 254, 254, 254, 254,
254, 254, 254, 254, 254, 250, 250, 252, 254, 254
},
{
231,
243,
245, 253, 254, 254, 254, 254, 254,
254, 254, 254, 254, 254, 251, 251, 254, 254, 254
}
};
/* Default MV decoding probabilities. */
const MV_CONTEXT default_mv_context[2] =
{
{ // row
162, // is short
128, // sign
225, 146, 172, 147, 214, 39, 156, // short tree
128, 129, 132, 75, 145, 178, 206, 239, 254, 254 // long bits
},
{ // same for column
164, // is short
128,
204, 170, 119, 235, 140, 230, 228,
128, 130, 130, 74, 148, 180, 203, 236, 254, 254 // long bits
}
};
/* Current MV decoding probabilities, set to above defaults
every key frame. */
MV_CONTEXT mvc [2]; /* always row, then column */
Bankoski, et al. Informational [Page 111]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/* Procedure for decoding a complete motion vector. */
typedef struct { int16 row, col;} MV; /* as in previous section */
MV read_mv(bool_decoder *d)
{
MV v;
v.row = (int16) read_mvcomponent(d, mvc);
v.col = (int16) read_mvcomponent(d, mvc + 1);
return v;
}
/* Procedure for updating MV decoding probabilities, called
every interframe with "d" at the appropriate position in
the frame header. */
void update_mvcontexts(bool_decoder *d)
{
int i = 0;
do { /* component = row, then column */
const Prob *up = mv_update_probs[i]; /* update probs
for component */
Prob *p = mvc[i]; /* start decode tbl "" */
Prob * const pstop = p + MVPcount; /* end decode tbl "" */
do {
if (read_bool(d, *up++)) /* update this position */
{
const Prob x = read_literal(d, 7);
*p = x? x<<1 : 1;
}
} while (++p < pstop); /* next position */
} while (++i < 2); /* next component */
}
---- End code block ----------------------------------------
This completes the description of the motion-vector decoding
procedure and, with it, the procedure for decoding interframe
macroblock prediction records.
Bankoski, et al. Informational [Page 112]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
18. Interframe Prediction
Given an inter-prediction specification for the current macroblock,
that is, a reference frame together with a motion vector for each of
the sixteen Y subblocks, we describe the calculation of the
prediction buffer for the macroblock. Frame reconstruction is then
completed via the previously described processes of residue summation
(Section 14) and loop filtering (Section 15).
The management of inter-predicted subblocks and sub-pixel
interpolation may be found in the reference decoder file predict.c
(Section 20.14).
18.1. Bounds on, and Adjustment of, Motion Vectors
Since each motion vector is differentially encoded from a neighboring
block or macroblock and the only clamp is to ensure that the
referenced motion vector represents a valid location inside a
reference frame buffer, it is technically possible within the VP8
format for a block or macroblock to have arbitrarily large motion
vectors, up to the size of the input image plus the extended border
areas. For practical reasons, VP8 imposes a motion vector size range
limit of -4096 to 4095 full pixels, regardless of image size (VP8
defines 14 raw bits for width and height; 16383x16383 is the maximum
possible image size). Bitstream-compliant encoders and decoders
shall enforce this limit.
Because the motion vectors applied to the chroma subblocks have
1/8-pixel resolution, the synthetic pixel calculation, outlined in
Section 5 and detailed below, uses this resolution for the luma
subblocks as well. In accordance, the stored luma motion vectors are
all doubled, each component of each luma vector becoming an even
integer in the range -2046 to +2046, inclusive.
The vector applied to each chroma subblock is calculated by averaging
the vectors for the 4 luma subblocks occupying the same visible area
as the chroma subblock in the usual correspondence; that is, the
vector for U and V block 0 is the average of the vectors for the Y
subblocks { 0, 1, 4, 5}, chroma block 1 corresponds to Y blocks { 2,
3, 6, 7}, chroma block 2 to Y blocks { 8, 9, 12, 13}, and chroma
block 3 to Y blocks { 10, 11, 14, 15}.
Bankoski, et al. Informational [Page 113]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
In detail, each of the two components of the vectors for each of the
chroma subblocks is calculated from the corresponding luma vector
components as follows:
---- Begin code block --------------------------------------
int avg(int c1, int c2, int c3, int c4)
{
int s = c1 + c2 + c3 + c4;
/* The shift divides by 8 (not 4) because chroma pixels
have twice the diameter of luma pixels. The handling
of negative motion vector components is slightly
cumbersome because, strictly speaking, right shifts
of negative numbers are not well-defined in C. */
return s >= 0 ? (s + 4) >> 3 : -((-s + 4) >> 3);
}
---- End code block ----------------------------------------
Furthermore, if the version number in the frame tag specifies only
full-pel chroma motion vectors, then the fractional parts of both
components of the vector are truncated to zero, as illustrated in the
following pseudocode (assuming 3 bits of fraction for both luma and
chroma vectors):
---- Begin code block --------------------------------------
x = x & (~7);
y = y & (~7);
---- End code block ----------------------------------------
Earlier in this document we described the vp8_clamp_mv() function to
limit "nearest" and "near" motion vector predictors inside specified
margins within the frame boundaries. Additional clamping is
performed for NEWMV macroblocks, for which the final motion vector is
clamped again after combining the "best" predictor and the
differential vector decoded from the stream.
However, the secondary clamping is not performed for SPLITMV
macroblocks, meaning that any subblock's motion vector within the
SPLITMV macroblock may point outside the clamping zone. These
non-clamped vectors are also used when determining the decoding tree
context for subsequent subblocks' modes in the vp8_mvCont() function.
Bankoski, et al. Informational [Page 114]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
18.2. Prediction Subblocks
The prediction calculation for each subblock is then as follows.
Temporarily disregarding the fractional part of the motion vector
(that is, rounding "up" or "left" by right-shifting each component
3 bits with sign propagation) and adding the origin (upper left
position) of the (16x16 luma or 8x8 chroma) current macroblock gives
us an origin in the Y, U, or V plane of the predictor frame (either
the golden frame or previous frame).
Considering that origin to be the upper left corner of a (luma or
chroma) macroblock, we need to specify the relative positions of the
pixels associated to that subblock, that is, any pixels that might be
involved in the sub-pixel interpolation processes for the subblock.
18.3. Sub-Pixel Interpolation
The sub-pixel interpolation is effected via two one-dimensional
convolutions. These convolutions may be thought of as operating on a
two-dimensional array of pixels whose origin is the subblock origin,
that is the origin of the prediction macroblock described above plus
the offset to the subblock. Because motion vectors are arbitrary, so
are these "prediction subblock origins".
The integer part of the motion vector is subsumed in the origin of
the prediction subblock; the 16 (synthetic) pixels we need to
construct are given by 16 offsets from the origin. The integer part
of each of these offsets is the offset of the corresponding pixel
from the subblock origin (using the vertical stride). To these
integer parts is added a constant fractional part, which is simply
the difference between the actual motion vector and its integer
truncation used to calculate the origins of the prediction macroblock
and subblock. Each component of this fractional part is an integer
between 0 and 7, representing a forward displacement in eighths of a
pixel.
It is these fractional displacements that determine the filtering
process. If they both happen to be zero (that is, we had a "whole
pixel" motion vector), the prediction subblock is simply copied into
the corresponding piece of the current macroblock's prediction
buffer. As discussed in Section 14, the layout of the macroblock's
prediction buffer can depend on the specifics of the reconstruction
implementation chosen. Of course, the vertical displacement between
lines of the prediction subblock is given by the stride, as are all
vertical displacements used here.
Bankoski, et al. Informational [Page 115]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
Otherwise, at least one of the fractional displacements is non-zero.
We then synthesize the missing pixels via a horizontal, followed by a
vertical, one-dimensional interpolation.
The two interpolations are essentially identical. Each uses a (at
most) six-tap filter (the choice of which of course depends on the
one-dimensional offset). Thus, every calculated pixel references at
most three pixels before (above or to the left of) it and at most
three pixels after (below or to the right of) it. The horizontal
interpolation must calculate two extra rows above and three extra
rows below the 4x4 block, to provide enough samples for the vertical
interpolation to proceed.
Depending on the reconstruction filter type given in the version
number field in the frame tag, either a bicubic or a bilinear tap set
is used.
The exact implementation of subsampling is as follows.
---- Begin code block --------------------------------------
/* Filter taps taken to 7-bit precision.
Because DC is always passed, taps always sum to 128. */
const int BilinearFilters[8][6] =
{
{ 0, 0, 128, 0, 0, 0 },
{ 0, 0, 112, 16, 0, 0 },
{ 0, 0, 96, 32, 0, 0 },
{ 0, 0, 80, 48, 0, 0 },
{ 0, 0, 64, 64, 0, 0 },
{ 0, 0, 48, 80, 0, 0 },
{ 0, 0, 32, 96, 0, 0 },
{ 0, 0, 16, 112, 0, 0 }
};
const int filters [8] [6] = { /* indexed by displacement */
{ 0, 0, 128, 0, 0, 0 }, /* degenerate whole-pixel */
{ 0, -6, 123, 12, -1, 0 }, /* 1/8 */
{ 2, -11, 108, 36, -8, 1 }, /* 1/4 */
{ 0, -9, 93, 50, -6, 0 }, /* 3/8 */
{ 3, -16, 77, 77, -16, 3 }, /* 1/2 is symmetric */
{ 0, -6, 50, 93, -9, 0 }, /* 5/8 = reverse of 3/8 */
{ 1, -8, 36, 108, -11, 2 }, /* 3/4 = reverse of 1/4 */
{ 0, -1, 12, 123, -6, 0 } /* 7/8 = reverse of 1/8 */
};
Bankoski, et al. Informational [Page 116]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/* One-dimensional synthesis of a single sample.
Filter is determined by fractional displacement */
Pixel interp(
const int fil[6], /* filter to apply */
const Pixel *p, /* origin (rounded "before") in
prediction area */
const int s /* size of one forward step "" */
) {
int32 a = 0;
int i = 0;
p -= s + s; /* move back two positions */
do {
a += *p * fil[i];
p += s;
} while (++i < 6);
return clamp255((a + 64) >> 7); /* round to nearest
8-bit value */
}
/* First do horizontal interpolation, producing intermediate
buffer. */
void Hinterp(
Pixel temp[9][4], /* 9 rows of 4 (intermediate)
destination values */
const Pixel *p, /* subblock origin in prediction
frame */
int s, /* vertical stride to be used in
prediction frame */
uint hfrac, /* 0 <= horizontal displacement <= 7 */
uint bicubic /* 1=bicubic filter, 0=bilinear */
) {
const int * const fil = bicubic ? filters [hfrac] :
BilinearFilters[hfrac];
int r = 0; do /* for each row */
{
int c = 0; do /* for each destination sample */
{
/* Pixel separation = one horizontal step = 1 */
temp[r][c] = interp(fil, p + c, 1);
}
Bankoski, et al. Informational [Page 117]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
while (++c < 4);
}
while (p += s, ++r < 9); /* advance p to next row */
}
/* Finish with vertical interpolation, producing final results.
Input array "temp" is of course that computed above. */
void Vinterp(
Pixel final[4][4], /* 4 rows of 4 (final) destination values */
const Pixel temp[9][4],
uint vfrac, /* 0 <= vertical displacement <= 7 */
uint bicubic /* 1=bicubic filter, 0=bilinear */
) {
const int * const fil = bicubic ? filters [vfrac] :
BilinearFilters[vfrac];
int r = 0; do /* for each row */
{
int c = 0; do /* for each destination sample */
{
/* Pixel separation = one vertical step = width
of array = 4 */
final[r][c] = interp(fil, temp[r] + c, 4);
}
while (++c < 4);
}
while (++r < 4);
}
---- End code block ----------------------------------------
18.4. Filter Properties
We discuss briefly the rationale behind the choice of filters. Our
approach is necessarily cursory; a genuinely accurate discussion
would require a couple of books. Readers unfamiliar with signal
processing may or may not wish to skip this.
All digital signals are of course sampled in some fashion. The case
where the inter-sample spacing (say in time for audio samples, or
space for pixels) is uniform, that is, the same at all positions, is
particularly common and amenable to analysis. Many aspects of the
treatment of such signals are best-understood in the frequency domain
via Fourier Analysis, particularly those aspects of the signal that
are not changed by shifts in position, especially when those
positional shifts are not given by a whole number of samples.
Bankoski, et al. Informational [Page 118]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
Non-integral translates of a sampled signal are a textbook example of
the foregoing. In our case of non-integral motion vectors, we wish
to say what the underlying image "really is" at these pixels;
although we don't have values for them, we feel that it makes sense
to talk about them. The correctness of this feeling is predicated on
the underlying signal being band-limited, that is, not containing any
energy in spatial frequencies that cannot be faithfully rendered at
the pixel resolution at our disposal. In one dimension, this range
of "OK" frequencies is called the Nyquist band; in our two-
dimensional case of integer-grid samples, this range might be termed
a Nyquist rectangle. The finer the grid, the more we know about the
image, and the wider the Nyquist rectangle.
It turns out that, for such band-limited signals, there is indeed an
exact mathematical formula to produce the correct sample value at an
arbitrary point. Unfortunately, this calculation requires the
consideration of every single sample in the image, as well as needing
to operate at infinite precision. Also, strictly speaking, all band-
limited signals have infinite spatial (or temporal) extent, so
everything we are discussing is really some sort of approximation.
It is true that the theoretically correct subsampling procedure, as
well as any approximation thereof, is always given by a translation-
invariant weighted sum (or filter) similar to that used by VP8. It
is also true that the reconstruction error made by such a filter can
be simply represented as a multiplier in the frequency domain; that
is, such filters simply multiply the Fourier transform of any signal
to which they are applied by a fixed function associated to the
filter. This fixed function is usually called the frequency response
(or transfer function); the ideal subsampling filter has a frequency
response equal to one in the Nyquist rectangle and zero everywhere
else.
Another basic fact about approximations to "truly correct"
subsampling is that the wider the subrectangle (within the Nyquist
rectangle) of spatial frequencies one wishes to "pass" (that is,
correctly render) or, put more accurately, the closer one wishes to
approximate the ideal transfer function, the more samples of the
original signal must be considered by the subsampling, and the wider
the calculation precision necessitated.
The filters chosen by VP8 were chosen, within the constraints of 4 or
6 taps and 7-bit precision, to do the best possible job of handling
the low spatial frequencies near the 0th DC frequency along with
introducing no resonances (places where the absolute value of the
frequency response exceeds one).
Bankoski, et al. Informational [Page 119]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
The justification for the foregoing has two parts. First, resonances
can produce extremely objectionable visible artifacts when, as often
happens in actual compressed video streams, filters are applied
repeatedly. Second, the vast majority of energy in real-world images
lies near DC and not at the high end.
To get slightly more specific, the filters chosen by VP8 are the best
resonance-free 4- or 6-tap filters possible, where "best" describes
the frequency response near the origin: The response at 0 is required
to be 1, and the graph of the response at 0 is as flat as possible.
To provide an intuitively more obvious point of reference, the "best"
2-tap filter is given by simple linear interpolation between the
surrounding actual pixels.
Finally, it should be noted that, because of the way motion vectors
are calculated, the (shorter) 4-tap filters (used for odd fractional
displacements) are applied in the chroma plane only. Human color
perception is notoriously poor, especially where higher spatial
frequencies are involved. The shorter filters are easier to
understand mathematically, and the difference between them and a
theoretically slightly better 6-tap filter is negligible where chroma
is concerned.
19. Annex A: Bitstream Syntax
This annex presents the bitstream syntax in a tabular form. All the
information elements have been introduced and explained in the
previous sections but are collected here for a quick reference. Each
syntax element is briefly described after the tabular representation
along with a reference to the corresponding paragraph in the main
document. The meaning of each syntax element value is not repeated
here.
The top-level hierarchy of the bitstream is introduced in Section 4.
Definition of syntax element coding types can be found in Section 8.
The types used in the representation in this annex are:
o f(n), n-bit value from stream (n successive bits, not boolean
encoded)
o L(n), n-bit number encoded as n booleans (with equal probability
of being 0 or 1)
o B(p), bool with probability p of being 0
o T, tree-encoded value
Bankoski, et al. Informational [Page 120]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
19.1. Uncompressed Data Chunk
| Frame Tag | Type |
| ------------------------------------------------- | ----- |
| frame_tag | f(24) |
| if (key_frame) { | |
| start_code | f(24) |
| horizontal_size_code | f(16) |
| vertical_size_code | f(16) |
| } | |
The 3-byte frame tag can be parsed as follows:
---- Begin code block --------------------------------------
unsigned char *c = pbi->source;
unsigned int tmp;
tmp = (c[2] << 16) | (c[1] << 8) | c[0];
key_frame = tmp & 0x1;
version = (tmp >> 1) & 0x7;
show_frame = (tmp >> 4) & 0x1;
first_part_size = (tmp >> 5) & 0x7FFFF;
---- End code block ----------------------------------------
Where:
o key_frame indicates whether the current frame is a key frame
or not.
o version determines the bitstream version.
o show_frame indicates whether the current frame is meant to be
displayed or not.
o first_part_size determines the size of the first partition
(control partition), excluding the uncompressed data chunk.
Bankoski, et al. Informational [Page 121]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
The start_code is a constant 3-byte pattern having value 0x9d012a.
The latter part of the uncompressed chunk (after the start_code) can
be parsed as follows:
---- Begin code block --------------------------------------
unsigned char *c = pbi->source + 6;
unsigned int tmp;
tmp = (c[1] << 8) | c[0];
width = tmp & 0x3FFF;
horizontal_scale = tmp >> 14;
tmp = (c[3] << 8) | c[2];
height = tmp & 0x3FFF;
vertical_scale = tmp >> 14;
---- End code block ----------------------------------------
19.2. Frame Header
| Frame Header | Type |
| ------------------------------------------------- | ----- |
| if (key_frame) { | |
| color_space | L(1) |
| clamping_type | L(1) |
| } | |
| segmentation_enabled | L(1) |
| if (segmentation_enabled) | |
| update_segmentation() | |
| filter_type | L(1) |
| loop_filter_level | L(6) |
| sharpness_level | L(3) |
| mb_lf_adjustments() | |
| log2_nbr_of_dct_partitions | L(2) |
| quant_indices() | |
| if (key_frame) | |
| refresh_entropy_probs | L(1) |
Bankoski, et al. Informational [Page 122]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
| else { | |
| refresh_golden_frame | L(1) |
| refresh_alternate_frame | L(1) |
| if (!refresh_golden_frame) | |
| copy_buffer_to_golden | L(2) |
| if (!refresh_alternate_frame) | |
| copy_buffer_to_alternate | L(2) |
| sign_bias_golden | L(1) |
| sign_bias_alternate | L(1) |
| refresh_entropy_probs | L(1) |
| refresh_last | L(1) |
| } | |
| token_prob_update() | |
| mb_no_skip_coeff | L(1) |
| if (mb_no_skip_coeff) | |
| prob_skip_false | L(8) |
| if (!key_frame) { | |
| prob_intra | L(8) |
| prob_last | L(8) |
| prob_gf | L(8) |
| intra_16x16_prob_update_flag | L(1) |
| if (intra_16x16_prob_update_flag) { | |
| for (i = 0; i < 4; i++) | |
| intra_16x16_prob | L(8) |
| } | |
| intra_chroma prob_update_flag | L(1) |
| if (intra_chroma_prob_update_flag) { | |
| for (i = 0; i < 3; i++) | |
| intra_chroma_prob | L(8) |
| } | |
| mv_prob_update() | |
| } | |
o color_space defines the YUV color space of the sequence
(Section 9.2)
o clamping_type specifies if the decoder is required to clamp the
reconstructed pixel values (Section 9.2)
o segmentation_enabled enables the segmentation feature for the
current frame (Section 9.3)
o filter_type determines whether the normal or the simple loop
filter is used (Sections 9.4, 15)
o loop_filter_level controls the deblocking filter
(Sections 9.4, 15)
Bankoski, et al. Informational [Page 123]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
o sharpness_level controls the deblocking filter (Sections 9.4, 15)
o log2_nbr_of_dct_partitions determines the number of separate
partitions containing the DCT coefficients of the macroblocks
(Section 9.5)
o refresh_entropy_probs determines whether updated token
probabilities are used only for this frame or until further update
o refresh_golden_frame determines if the current decoded frame
refreshes the golden frame (Section 9.7)
o refresh_alternate_frame determines if the current decoded frame
refreshes the alternate reference frame (Section 9.7)
o copy_buffer_to_golden determines if the golden reference is
replaced by another reference (Section 9.7)
o copy_buffer_to_alternate determines if the alternate reference is
replaced by another reference (Section 9.7)
o sign_bias_golden controls the sign of motion vectors when the
golden frame is referenced (Section 9.7)
o sign_bias_alternate controls the sign of motion vectors when the
alternate frame is referenced (Section 9.7)
o refresh_last determines if the current decoded frame refreshes the
last frame reference buffer (Section 9.8)
o mb_no_skip_coeff enables or disables the skipping of macroblocks
containing no non-zero coefficients (Section 9.10)
o prob_skip_false indicates the probability that the macroblock is
not skipped (flag indicating skipped macroblock is false)
(Section 9.10)
o prob_intra indicates the probability of an intra macroblock
(Section 9.10)
o prob_last indicates the probability that the last reference frame
is used for inter-prediction (Section 9.10)
o prob_gf indicates the probability that the golden reference frame
is used for inter-prediction (Section 9.10)
Bankoski, et al. Informational [Page 124]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
o intra_16x16_prob_update_flag indicates if the branch probabilities
used in the decoding of the luma intra-prediction mode are updated
(Section 9.10)
o intra_16x16_prob indicates the branch probabilities of the luma
intra-prediction mode decoding tree
o intra_chroma_prob_update_flag indicates if the branch
probabilities used in the decoding of the chroma intra-prediction
mode are updated (Section 9.10)
o intra_chroma_prob indicates the branch probabilities of the chroma
intra-prediction mode decoding tree
| update_segmentation() | Type |
| ------------------------------------------------- | ----- |
| update_mb_segmentation_map | L(1) |
| update_segment_feature_data | L(1) |
| if (update_segment_feature_data) { | |
| segment_feature_mode | L(1) |
| for (i = 0; i < 4; i++) { | |
| quantizer_update | L(1) |
| if (quantizer_update) { | |
| quantizer_update_value | L(7) |
| quantizer_update_sign | L(1) |
| } | |
| } | |
| for (i = 0; i < 4; i++) { | |
| loop_filter_update | L(1) |
| if (loop_filter_update) { | |
| lf_update_value | L(6) |
| lf_update_sign | L(1) |
| } | |
| } | |
| } | |
| if (update_mb_segmentation_map) { | |
| for (i = 0; i < 3; i++) { | |
| segment_prob_update | L(1) |
| if (segment_prob_update) | |
| segment_prob | L(8) |
| } | |
| } | |
o update_mb_segmentation_map determines if the MB segmentation map
is updated in the current frame (Section 9.3)
o update_segment_feature_data indicates if the segment feature data
is updated in the current frame (Section 9.3)
Bankoski, et al. Informational [Page 125]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
o segment_feature_mode indicates the feature data update mode, 0 for
delta and 1 for the absolute value (Section 9.3)
o quantizer_update indicates if the quantizer value is updated for
the i^(th) segment (Section 9.3)
o quantizer_update_value indicates the update value for the segment
quantizer (Section 9.3)
o quantizer_update_sign indicates the update sign for the segment
quantizer (Section 9.3)
o loop_filter_update indicates if the loop filter level value is
updated for the i^(th) segment (Section 9.3)
o lf_update_value indicates the update value for the loop filter
level (Section 9.3)
o lf_update_sign indicates the update sign for the loop filter level
(Section 9.3)
o segment_prob_update indicates whether the branch probabilities
used to decode the segment_id in the MB header are decoded from
the stream or use the default value of 255 (Section 9.3)
o segment_prob indicates the branch probabilities of the segment_id
decoding tree (Section 9.3)
Bankoski, et al. Informational [Page 126]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
| mb_lf_adjustments() | Type |
| ------------------------------------------------- | ----- |
| loop_filter_adj_enable | L(1) |
| if (loop_filter_adj_enable) { | |
| mode_ref_lf_delta_update | L(1) |
| if (mode_ref_lf_delta_update) { | |
| for (i = 0; i < 4; i++) { | |
| ref_frame_delta_update_flag | L(1) |
| if (ref_frame_delta_update_flag) { | |
| delta_magnitude | L(6) |
| delta_sign | L(1) |
| } | |
| } | |
| for (i = 0; i < 4; i++) { | |
| mb_mode_delta_update_flag | L(1) |
| if (mb_mode_delta_update_flag) { | |
| delta_magnitude | L(6) |
| delta_sign | L(1) |
| } | |
| } | |
| } | |
| } | |
o loop_filter_adj_enable indicates if the MB-level loop filter
adjustment (based on the used reference frame and coding mode) is
on for the current frame (Section 9.4)
o mode_ref_lf_delta_update indicates if the delta values used in an
adjustment are updated in the current frame (Section 9.4)
o ref_frame_delta_update_flag indicates if the adjustment delta
value corresponding to a certain used reference frame is updated
(Section 9.4)
o delta_magnitude is the absolute value of the delta value
o delta_sign is the sign of the delta value
o mb_mode_delta_update_flag indicates if the adjustment delta value
corresponding to a certain MB prediction mode is updated
(Section 9.4)
Bankoski, et al. Informational [Page 127]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
| quant_indices() | Type |
| ------------------------------------------------- | ----- |
| y_ac_qi | L(7) |
| y_dc_delta_present | L(1) |
| if (y_dc_delta_present) { | |
| y_dc_delta_magnitude | L(4) |
| y_dc_delta_sign | L(1) |
| } | |
| y2_dc_delta_present | L(1) |
| if (y2_dc_delta_present) { | |
| y2_dc_delta_magnitude | L(4) |
| y2_dc_delta_sign | L(1) |
| } | |
| y2_ac_delta_present | L(1) |
| if (y2_ac_delta_present) { | |
| y2_ac_delta_magnitude | L(4) |
| y2_ac_delta_sign | L(1) |
| } | |
| uv_dc_delta_present | L(1) |
| if (uv_dc_delta_present) { | |
| uv_dc_delta_magnitude | L(4) |
| uv_dc_delta_sign | L(1) |
| } | |
| uv_ac_delta_present | L(1) |
| if (uv_ac_delta_present) { | |
| uv_ac_delta_magnitude | L(4) |
| uv_ac_delta_sign | L(1) |
| } | |
o y_ac_qi is the dequantization table index used for the luma AC
coefficients (and other coefficient groups if no delta value is
present) (Section 9.6)
o y_dc_delta_present indicates if the stream contains a delta value
that is added to the baseline index to obtain the luma DC
coefficient dequantization index (Section 9.6)
o y_dc_delta_magnitude is the magnitude of the delta value
(Section 9.6)
o y_dc_delta_sign is the sign of the delta value (Section 9.6)
o y2_dc_delta_present indicates if the stream contains a delta value
that is added to the baseline index to obtain the Y2 block DC
coefficient dequantization index (Section 9.6)
Bankoski, et al. Informational [Page 128]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
o y2_ac_delta_present indicates if the stream contains a delta value
that is added to the baseline index to obtain the Y2 block AC
coefficient dequantization index (Section 9.6)
o uv_dc_delta_present indicates if the stream contains a delta value
that is added to the baseline index to obtain the chroma DC
coefficient dequantization index (Section 9.6)
o uv_ac_delta_present indicates if the stream contains a delta value
that is added to the baseline index to obtain the chroma AC
coefficient dequantization index (Section 9.6)
| token_prob_update() | Type |
| ------------------------------------------------- | ----- |
| for (i = 0; i < 4; i++) { | |
| for (j = 0; j < 8; j++) { | |
| for (k = 0; k < 3; k++) { | |
| for (l = 0; l < 11; l++) { | |
| coeff_prob_update_flag | L(1) |
| if (coeff_prob_update_flag) | |
| coeff_prob | L(8) |
| } | |
| } | |
| } | |
| } | |
o coeff_prob_update_flag indicates if the corresponding branch
probability is updated in the current frame (Section 13.4)
o coeff_prob is the new branch probability (Section 13.4)
| mv_prob_update() | Type |
| ------------------------------------------------- | ----- |
| for (i = 0; i < 2; i++) { | |
| for (j = 0; j < 19; j++) { | |
| mv_prob_update_flag | L(1) |
| if (mv_prob_update_flag) | |
| prob | L(7) |
| } | |
| } | |
o mv_prob_update_flag indicates if the corresponding MV decoding
probability is updated in the current frame (Section 17.2)
o prob is the updated probability (Section 17.2)
Bankoski, et al. Informational [Page 129]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
19.3. Macroblock Data
| Macroblock Data | Type |
| ------------------------------------------------- | ----- |
| macroblock_header() | |
| residual_data() | |
| macroblock_header() | Type |
| ------------------------------------------------- | ----- |
| if (update_mb_segmentation_map) | |
| segment_id | T |
| if (mb_no_skip_coeff) | |
| mb_skip_coeff | B(p) |
| if (!key_frame) | |
| is_inter_mb | B(p) |
| if (is_inter_mb) { | |
| mb_ref_frame_sel1 | B(p) |
| if (mb_ref_frame_sel1) | |
| mb_ref_frame_sel2 | B(p) |
| mv_mode | T |
| if (mv_mode == SPLITMV) { | |
| mv_split_mode | T |
| for (i = 0; i < numMvs; i++) { | |
| sub_mv_mode | T |
| if (sub_mv_mode == NEWMV4x4) { | |
| read_mvcomponent() | |
| read_mvcomponent() | |
| } | |
| } | |
| } else if (mv_mode == NEWMV) { | |
| read_mvcomponent() | |
| read_mvcomponent() | |
| } | |
| } else { /* intra mb */ | |
| intra_y_mode | T |
| if (intra_y_mode == B_PRED) { | |
| for (i = 0; i < 16; i++) | |
| intra_b_mode | T |
| } | |
| intra_uv_mode | T |
| } | |
o segment_id indicates to which segment the macroblock belongs
(Section 10)
o mb_skip_coeff indicates whether the macroblock contains any coded
coefficients or not (Section 11.1)
Bankoski, et al. Informational [Page 130]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
o is_inter_mb indicates whether the macroblock is intra- or inter-
coded (Section 16)
o mb_ref_frame_sel1 selects the reference frame to be used; last
frame (0), golden/alternate (1) (Section 16.2)
o mb_ref_frame_sel2 selects whether the golden (0) or alternate
reference frame (1) is used (Section 16.2)
o mv_mode determines the macroblock motion vector mode
(Section 16.2)
o mv_split_mode gives the macroblock partitioning specification and
determines the number of motion vectors used (numMvs)
(Section 16.2)
o sub_mv_mode determines the sub-macroblock motion vector mode for
macroblocks coded using the SPLITMV motion vector mode
(Section 16.2)
o intra_y_mode selects the luminance intra-prediction mode
(Section 16.1)
o intra_b_mode selects the sub-macroblock luminance prediction mode
for macroblocks coded using B_PRED mode (Section 16.1)
o intra_uv_mode selects the chrominance intra-prediction mode
(Section 16.1)
| residual_data() | Type |
| ------------------------------------------------- | ----- |
| if (!mb_skip_coeff) { | |
| if ( (is_inter_mb && mv_mode != SPLITMV) || | |
| (!is_inter_mb && intra_y_mode != B_PRED) ) | |
| residual_block() /* Y2 */ | |
| for (i = 0; i < 24; i++) | |
| residual_block() /* 16 Y, 4 U, 4 V */ | |
| } | |
Bankoski, et al. Informational [Page 131]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
| residual_block() | Type |
| ------------------------------------------------- | ----- |
| for (i = firstCoeff; i < 16; i++) { | |
| token | T |
| if (token == EOB) break; | |
| if (token_has_extra_bits) | |
| extra_bits | L(n) |
| if (coefficient != 0) | |
| sign | L(1) |
| } | |
o firstCoeff is 1 for luma blocks of macroblocks containing Y2
subblock; otherwise 0
o token defines the value of the coefficient, the value range of the
coefficient, or the end of block (Section 13.2)
o extra_bits determines the value of the coefficient within the
value range defined by the token (Section 13.2)
o sign indicates the sign of the coefficient (Section 13.2)
Bankoski, et al. Informational [Page 132]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
20. Attachment One: Reference Decoder Source Code
20.1. bit_ops.h
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#ifndef BIT_OPS_H
#define BIT_OPS_H
/* Evaluates to a mask with n bits set */
#define BITS_MASK(n) ((1<<(n))-1)
/* Returns len bits, with the LSB at position bit */
#define BITS_GET(val, bit, len) (((val)>>(bit))&BITS_MASK(len))
#endif
---- End code block ----------------------------------------
20.2. bool_decoder.h
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#ifndef BOOL_DECODER_H
#define BOOL_DECODER_H
#include <stddef.h>
Bankoski, et al. Informational [Page 133]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
struct bool_decoder
{
const unsigned char *input; /* next compressed data byte */
size_t input_len; /* length of the input buffer */
unsigned int range; /* identical to encoder's
* range */
unsigned int value; /* contains at least 8
* significant bits */
int bit_count; /* # of bits shifted out of
* value, max 7 */
};
static void
init_bool_decoder(struct bool_decoder *d,
const unsigned char *start_partition,
size_t sz)
{
if (sz >= 2)
{
d->value = (start_partition[0] << 8) /* first 2 input
* bytes */
| start_partition[1];
d->input = start_partition + 2; /* ptr to next byte */
d->input_len = sz - 2;
}
else
{
d->value = 0;
d->input = NULL;
d->input_len = 0;
}
d->range = 255; /* initial range is full */
d->bit_count = 0; /* have not yet shifted out any bits */
}
static int bool_get(struct bool_decoder *d, int probability)
{
/* range and split are identical to the corresponding values
used by the encoder when this bool was written */
unsigned int split = 1 + (((d->range - 1) * probability) >> 8);
unsigned int SPLIT = split << 8;
int retval; /* will be 0 or 1 */
Bankoski, et al. Informational [Page 134]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
if (d->value >= SPLIT) /* encoded a one */
{
retval = 1;
d->range -= split; /* reduce range */
d->value -= SPLIT; /* subtract off left endpoint of
* interval */
}
else /* encoded a zero */
{
retval = 0;
d->range = split; /* reduce range, no change in left
* endpoint */
}
while (d->range < 128) /* shift out irrelevant value bits */
{
d->value <<= 1;
d->range <<= 1;
if (++d->bit_count == 8) /* shift in new bits 8 at a time */
{
d->bit_count = 0;
if (d->input_len)
{
d->value |= *d->input++;
d->input_len--;
}
}
}
return retval;
}
static int bool_get_bit(struct bool_decoder *br)
{
return bool_get(br, 128);
}
Bankoski, et al. Informational [Page 135]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static int bool_get_uint(struct bool_decoder *br, int bits)
{
int z = 0;
int bit;
for (bit = bits - 1; bit >= 0; bit--)
{
z |= (bool_get_bit(br) << bit);
}
return z;
}
static int bool_get_int(struct bool_decoder *br, int bits)
{
int z = 0;
int bit;
for (bit = bits - 1; bit >= 0; bit--)
{
z |= (bool_get_bit(br) << bit);
}
return bool_get_bit(br) ? -z : z;
}
static int bool_maybe_get_int(struct bool_decoder *br, int bits)
{
return bool_get_bit(br) ? bool_get_int(br, bits) : 0;
}
static int
bool_read_tree(struct bool_decoder *bool,
const int *t,
const unsigned char *p)
{
int i = 0;
while ((i = t[ i + bool_get(bool, p[i>>1])]) > 0);
return -i;
}
#endif
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 136]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
20.3. dequant_data.h
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
static const int dc_q_lookup[128] =
{
4, 5, 6, 7, 8, 9, 10, 10,
11, 12, 13, 14, 15, 16, 17, 17,
18, 19, 20, 20, 21, 21, 22, 22,
23, 23, 24, 25, 25, 26, 27, 28,
29, 30, 31, 32, 33, 34, 35, 36,
37, 37, 38, 39, 40, 41, 42, 43,
44, 45, 46, 46, 47, 48, 49, 50,
51, 52, 53, 54, 55, 56, 57, 58,
59, 60, 61, 62, 63, 64, 65, 66,
67, 68, 69, 70, 71, 72, 73, 74,
75, 76, 76, 77, 78, 79, 80, 81,
82, 83, 84, 85, 86, 87, 88, 89,
91, 93, 95, 96, 98, 100, 101, 102,
104, 106, 108, 110, 112, 114, 116, 118,
122, 124, 126, 128, 130, 132, 134, 136,
138, 140, 143, 145, 148, 151, 154, 157
};
static const int ac_q_lookup[128] =
{
4, 5, 6, 7, 8, 9, 10, 11,
12, 13, 14, 15, 16, 17, 18, 19,
20, 21, 22, 23, 24, 25, 26, 27,
28, 29, 30, 31, 32, 33, 34, 35,
36, 37, 38, 39, 40, 41, 42, 43,
44, 45, 46, 47, 48, 49, 50, 51,
52, 53, 54, 55, 56, 57, 58, 60,
62, 64, 66, 68, 70, 72, 74, 76,
78, 80, 82, 84, 86, 88, 90, 92,
94, 96, 98, 100, 102, 104, 106, 108,
110, 112, 114, 116, 119, 122, 125, 128,
131, 134, 137, 140, 143, 146, 149, 152,
Bankoski, et al. Informational [Page 137]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
155, 158, 161, 164, 167, 170, 173, 177,
181, 185, 189, 193, 197, 201, 205, 209,
213, 217, 221, 225, 229, 234, 239, 245,
249, 254, 259, 264, 269, 274, 279, 284
};
---- End code block ----------------------------------------
20.4. dixie.c
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#include "vpx_codec_internal.h"
#include "bit_ops.h"
#include "dixie.h"
#include "vp8_prob_data.h"
#include "dequant_data.h"
#include "modemv.h"
#include "tokens.h"
#include "predict.h"
#include "dixie_loopfilter.h"
#include <string.h>
#include <assert.h>
enum
{
FRAME_HEADER_SZ = 3,
KEYFRAME_HEADER_SZ = 7
};
#define ARRAY_COPY(a,b) {\
assert(sizeof(a)==sizeof(b));memcpy(a,b,sizeof(a));}
static void
decode_entropy_header(struct vp8_decoder_ctx *ctx,
struct bool_decoder *bool,
struct vp8_entropy_hdr *hdr)
Bankoski, et al. Informational [Page 138]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{
int i, j, k, l;
/* Read coefficient probability updates */
for (i = 0; i < BLOCK_TYPES; i++)
for (j = 0; j < COEFF_BANDS; j++)
for (k = 0; k < PREV_COEFF_CONTEXTS; k++)
for (l = 0; l < ENTROPY_NODES; l++)
if (bool_get(bool,
k_coeff_entropy_update_probs
[i][j][k][l]))
hdr->coeff_probs[i][j][k][l] =
bool_get_uint(bool, 8);
/* Read coefficient skip mode probability */
hdr->coeff_skip_enabled = bool_get_bit(bool);
if (hdr->coeff_skip_enabled)
hdr->coeff_skip_prob = bool_get_uint(bool, 8);
/* Parse interframe probability updates */
if (!ctx->frame_hdr.is_keyframe)
{
hdr->prob_inter = bool_get_uint(bool, 8);
hdr->prob_last = bool_get_uint(bool, 8);
hdr->prob_gf = bool_get_uint(bool, 8);
if (bool_get_bit(bool))
for (i = 0; i < 4; i++)
hdr->y_mode_probs[i] = bool_get_uint(bool, 8);
if (bool_get_bit(bool))
for (i = 0; i < 3; i++)
hdr->uv_mode_probs[i] = bool_get_uint(bool, 8);
for (i = 0; i < 2; i++)
for (j = 0; j < MV_PROB_CNT; j++)
if (bool_get(bool, k_mv_entropy_update_probs[i][j]))
{
int x = bool_get_uint(bool, 7);
hdr->mv_probs[i][j] = x ? x << 1 : 1;
}
}
}
Bankoski, et al. Informational [Page 139]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static void
decode_reference_header(struct vp8_decoder_ctx *ctx,
struct bool_decoder *bool,
struct vp8_reference_hdr *hdr)
{
unsigned int key = ctx->frame_hdr.is_keyframe;
hdr->refresh_gf = key ? 1 : bool_get_bit(bool);
hdr->refresh_arf = key ? 1 : bool_get_bit(bool);
hdr->copy_gf = key ? 0 : !hdr->refresh_gf
? bool_get_uint(bool, 2) : 0;
hdr->copy_arf = key ? 0 : !hdr->refresh_arf
? bool_get_uint(bool, 2) : 0;
hdr->sign_bias[GOLDEN_FRAME] = key ? 0 : bool_get_bit(bool);
hdr->sign_bias[ALTREF_FRAME] = key ? 0 : bool_get_bit(bool);
hdr->refresh_entropy = bool_get_bit(bool);
hdr->refresh_last = key ? 1 : bool_get_bit(bool);
}
static void
decode_quantizer_header(struct vp8_decoder_ctx *ctx,
struct bool_decoder *bool,
struct vp8_quant_hdr *hdr)
{
int update;
int last_q = hdr->q_index;
hdr->q_index = bool_get_uint(bool, 7);
update = last_q != hdr->q_index;
update |= (hdr->y1_dc_delta_q = bool_maybe_get_int(bool, 4));
update |= (hdr->y2_dc_delta_q = bool_maybe_get_int(bool, 4));
update |= (hdr->y2_ac_delta_q = bool_maybe_get_int(bool, 4));
update |= (hdr->uv_dc_delta_q = bool_maybe_get_int(bool, 4));
update |= (hdr->uv_ac_delta_q = bool_maybe_get_int(bool, 4));
hdr->delta_update = update;
}
static void
decode_and_init_token_partitions(struct vp8_decoder_ctx *ctx,
struct bool_decoder *bool,
const unsigned char *data,
unsigned int sz,
struct vp8_token_hdr *hdr)
Bankoski, et al. Informational [Page 140]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{
int i;
hdr->partitions = 1 << bool_get_uint(bool, 2);
if (sz < 3 *(hdr->partitions - 1))
vpx_internal_error(&ctx->error, VPX_CODEC_CORRUPT_FRAME,
"Truncated packet found parsing partition"
" lengths.");
sz -= 3 * (hdr->partitions - 1);
for (i = 0; i < hdr->partitions; i++)
{
if (i < hdr->partitions - 1)
{
hdr->partition_sz[i] = (data[2] << 16)
| (data[1] << 8) | data[0];
data += 3;
}
else
hdr->partition_sz[i] = sz;
if (sz < hdr->partition_sz[i])
vpx_internal_error(&ctx->error, VPX_CODEC_CORRUPT_FRAME,
"Truncated partition %d", i);
sz -= hdr->partition_sz[i];
}
for (i = 0; i < ctx->token_hdr.partitions; i++)
{
init_bool_decoder(&ctx->tokens[i].bool, data,
ctx->token_hdr.partition_sz[i]);
data += ctx->token_hdr.partition_sz[i];
}
}
static void
decode_loopfilter_header(struct vp8_decoder_ctx *ctx,
struct bool_decoder *bool,
struct vp8_loopfilter_hdr *hdr)
Bankoski, et al. Informational [Page 141]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{
if (ctx->frame_hdr.is_keyframe)
memset(hdr, 0, sizeof(*hdr));
hdr->use_simple = bool_get_bit(bool);
hdr->level = bool_get_uint(bool, 6);
hdr->sharpness = bool_get_uint(bool, 3);
hdr->delta_enabled = bool_get_bit(bool);
if (hdr->delta_enabled && bool_get_bit(bool))
{
int i;
for (i = 0; i < BLOCK_CONTEXTS; i++)
hdr->ref_delta[i] = bool_maybe_get_int(bool, 6);
for (i = 0; i < BLOCK_CONTEXTS; i++)
hdr->mode_delta[i] = bool_maybe_get_int(bool, 6);
}
}
static void
decode_segmentation_header(struct vp8_decoder_ctx *ctx,
struct bool_decoder *bool,
struct vp8_segment_hdr *hdr)
{
if (ctx->frame_hdr.is_keyframe)
memset(hdr, 0, sizeof(*hdr));
hdr->enabled = bool_get_bit(bool);
if (hdr->enabled)
{
int i;
hdr->update_map = bool_get_bit(bool);
hdr->update_data = bool_get_bit(bool);
Bankoski, et al. Informational [Page 142]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
if (hdr->update_data)
{
hdr->abs = bool_get_bit(bool);
for (i = 0; i < MAX_MB_SEGMENTS; i++)
hdr->quant_idx[i] = bool_maybe_get_int(bool, 7);
for (i = 0; i < MAX_MB_SEGMENTS; i++)
hdr->lf_level[i] = bool_maybe_get_int(bool, 6);
}
if (hdr->update_map)
{
for (i = 0; i < MB_FEATURE_TREE_PROBS; i++)
hdr->tree_probs[i] = bool_get_bit(bool)
? bool_get_uint(bool, 8)
: 255;
}
}
else
{
hdr->update_map = 0;
hdr->update_data = 0;
}
}
static void
dequant_global_init(struct dequant_factors dqf[MAX_MB_SEGMENTS])
{
int i;
for (i = 0; i < MAX_MB_SEGMENTS; i++)
dqf[i].quant_idx = -1;
}
static int
clamp_q(int q)
{
if (q < 0) return 0;
else if (q > 127) return 127;
return q;
}
Bankoski, et al. Informational [Page 143]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static int
dc_q(int q)
{
return dc_q_lookup[clamp_q(q)];
}
static int
ac_q(int q)
{
return ac_q_lookup[clamp_q(q)];
}
static void
dequant_init(struct dequant_factors factors[MAX_MB_SEGMENTS],
const struct vp8_segment_hdr *seg,
const struct vp8_quant_hdr *quant_hdr)
{
int i, q;
struct dequant_factors *dqf = factors;
for (i = 0; i < (seg->enabled ? MAX_MB_SEGMENTS : 1); i++)
{
q = quant_hdr->q_index;
if (seg->enabled)
q = (!seg->abs) ? q + seg->quant_idx[i]
: seg->quant_idx[i];
if (dqf->quant_idx != q || quant_hdr->delta_update)
{
dqf->factor[TOKEN_BLOCK_Y1][0] =
dc_q(q + quant_hdr->y1_dc_delta_q);
dqf->factor[TOKEN_BLOCK_Y1][1] =
ac_q(q);
dqf->factor[TOKEN_BLOCK_UV][0] =
dc_q(q + quant_hdr->uv_dc_delta_q);
dqf->factor[TOKEN_BLOCK_UV][1] =
ac_q(q + quant_hdr->uv_ac_delta_q);
dqf->factor[TOKEN_BLOCK_Y2][0] =
dc_q(q + quant_hdr->y2_dc_delta_q) * 2;
dqf->factor[TOKEN_BLOCK_Y2][1] =
ac_q(q + quant_hdr->y2_ac_delta_q) * 155 / 100;
if (dqf->factor[TOKEN_BLOCK_Y2][1] < 8)
dqf->factor[TOKEN_BLOCK_Y2][1] = 8;
Bankoski, et al. Informational [Page 144]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
if (dqf->factor[TOKEN_BLOCK_UV][0] > 132)
dqf->factor[TOKEN_BLOCK_UV][0] = 132;
dqf->quant_idx = q;
}
dqf++;
}
}
static void
decode_frame(struct vp8_decoder_ctx *ctx,
const unsigned char *data,
unsigned int sz)
{
vpx_codec_err_t res;
struct bool_decoder bool;
int i, row, partition;
ctx->saved_entropy_valid = 0;
if ((res = vp8_parse_frame_header(data, sz, &ctx->frame_hdr)))
vpx_internal_error(&ctx->error, res,
"Failed to parse frame header");
if (ctx->frame_hdr.is_experimental)
vpx_internal_error(&ctx->error, VPX_CODEC_UNSUP_BITSTREAM,
"Experimental bitstreams not supported.");
data += FRAME_HEADER_SZ;
sz -= FRAME_HEADER_SZ;
if (ctx->frame_hdr.is_keyframe)
{
data += KEYFRAME_HEADER_SZ;
sz -= KEYFRAME_HEADER_SZ;
ctx->mb_cols = (ctx->frame_hdr.kf.w + 15) / 16;
ctx->mb_rows = (ctx->frame_hdr.kf.h + 15) / 16;
}
/* Start the bitreader for the header/entropy partition */
init_bool_decoder(&bool, data, ctx->frame_hdr.part0_sz);
Bankoski, et al. Informational [Page 145]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/* Skip the colorspace and clamping bits */
if (ctx->frame_hdr.is_keyframe)
if (bool_get_uint(&bool, 2))
vpx_internal_error(
&ctx->error, VPX_CODEC_UNSUP_BITSTREAM,
"Reserved bits not supported.");
decode_segmentation_header(ctx, &bool, &ctx->segment_hdr);
decode_loopfilter_header(ctx, &bool, &ctx->loopfilter_hdr);
decode_and_init_token_partitions(ctx,
&bool,
data + ctx->frame_hdr.part0_sz,
sz - ctx->frame_hdr.part0_sz,
&ctx->token_hdr);
decode_quantizer_header(ctx, &bool, &ctx->quant_hdr);
decode_reference_header(ctx, &bool, &ctx->reference_hdr);
/* Set keyframe entropy defaults. These get updated on keyframes
* regardless of the refresh_entropy setting.
*/
if (ctx->frame_hdr.is_keyframe)
{
ARRAY_COPY(ctx->entropy_hdr.coeff_probs,
k_default_coeff_probs);
ARRAY_COPY(ctx->entropy_hdr.mv_probs,
k_default_mv_probs);
ARRAY_COPY(ctx->entropy_hdr.y_mode_probs,
k_default_y_mode_probs);
ARRAY_COPY(ctx->entropy_hdr.uv_mode_probs,
k_default_uv_mode_probs);
}
if (!ctx->reference_hdr.refresh_entropy)
{
ctx->saved_entropy = ctx->entropy_hdr;
ctx->saved_entropy_valid = 1;
}
decode_entropy_header(ctx, &bool, &ctx->entropy_hdr);
vp8_dixie_modemv_init(ctx);
vp8_dixie_tokens_init(ctx);
vp8_dixie_predict_init(ctx);
dequant_init(ctx->dequant_factors, &ctx->segment_hdr,
&ctx->quant_hdr);
Bankoski, et al. Informational [Page 146]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
for (row = 0, partition = 0; row < ctx->mb_rows; row++)
{
vp8_dixie_modemv_process_row(
ctx, &bool, row, 0, ctx->mb_cols);
vp8_dixie_tokens_process_row(ctx, partition, row, 0,
ctx->mb_cols);
vp8_dixie_predict_process_row(ctx, row, 0, ctx->mb_cols);
if (ctx->loopfilter_hdr.level && row)
vp8_dixie_loopfilter_process_row(ctx, row - 1, 0,
ctx->mb_cols);
if (++partition == ctx->token_hdr.partitions)
partition = 0;
}
if (ctx->loopfilter_hdr.level)
vp8_dixie_loopfilter_process_row(
ctx, row - 1, 0, ctx->mb_cols);
ctx->frame_cnt++;
if (!ctx->reference_hdr.refresh_entropy)
{
ctx->entropy_hdr = ctx->saved_entropy;
ctx->saved_entropy_valid = 0;
}
/* Handle reference frame updates */
if (ctx->reference_hdr.copy_arf == 1)
{
vp8_dixie_release_ref_frame(ctx->ref_frames[ALTREF_FRAME]);
ctx->ref_frames[ALTREF_FRAME] =
vp8_dixie_ref_frame(ctx->ref_frames[LAST_FRAME]);
}
else if (ctx->reference_hdr.copy_arf == 2)
{
vp8_dixie_release_ref_frame(ctx->ref_frames[ALTREF_FRAME]);
ctx->ref_frames[ALTREF_FRAME] =
vp8_dixie_ref_frame(ctx->ref_frames[GOLDEN_FRAME]);
}
if (ctx->reference_hdr.copy_gf == 1)
{
vp8_dixie_release_ref_frame(ctx->ref_frames[GOLDEN_FRAME]);
ctx->ref_frames[GOLDEN_FRAME] =
vp8_dixie_ref_frame(ctx->ref_frames[LAST_FRAME]);
}
Bankoski, et al. Informational [Page 147]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
else if (ctx->reference_hdr.copy_gf == 2)
{
vp8_dixie_release_ref_frame(ctx->ref_frames[GOLDEN_FRAME]);
ctx->ref_frames[GOLDEN_FRAME] =
vp8_dixie_ref_frame(ctx->ref_frames[ALTREF_FRAME]);
}
if (ctx->reference_hdr.refresh_gf)
{
vp8_dixie_release_ref_frame(ctx->ref_frames[GOLDEN_FRAME]);
ctx->ref_frames[GOLDEN_FRAME] =
vp8_dixie_ref_frame(ctx->ref_frames[CURRENT_FRAME]);
}
if (ctx->reference_hdr.refresh_arf)
{
vp8_dixie_release_ref_frame(ctx->ref_frames[ALTREF_FRAME]);
ctx->ref_frames[ALTREF_FRAME] =
vp8_dixie_ref_frame(ctx->ref_frames[CURRENT_FRAME]);
}
if (ctx->reference_hdr.refresh_last)
{
vp8_dixie_release_ref_frame(ctx->ref_frames[LAST_FRAME]);
ctx->ref_frames[LAST_FRAME] =
vp8_dixie_ref_frame(ctx->ref_frames[CURRENT_FRAME]);
}
}
void
vp8_dixie_decode_init(struct vp8_decoder_ctx *ctx)
{
dequant_global_init(ctx->dequant_factors);
}
Bankoski, et al. Informational [Page 148]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
#define CHECK_FOR_UPDATE(lval,rval,update_flag) do {\
unsigned int old = lval; \
update_flag |= (old != (lval = rval)); \
} while (0)
vpx_codec_err_t
vp8_parse_frame_header(const unsigned char *data,
unsigned int sz,
struct vp8_frame_hdr *hdr)
{
unsigned long raw;
if (sz < 10)
return VPX_CODEC_CORRUPT_FRAME;
/* The frame header is defined as a three-byte little endian
* value
*/
raw = data[0] | (data[1] << 8) | (data[2] << 16);
hdr->is_keyframe = !BITS_GET(raw, 0, 1);
hdr->version = BITS_GET(raw, 1, 2);
hdr->is_experimental = BITS_GET(raw, 3, 1);
hdr->is_shown = BITS_GET(raw, 4, 1);
hdr->part0_sz = BITS_GET(raw, 5, 19);
if (sz <= hdr->part0_sz + (hdr->is_keyframe ? 10 : 3))
return VPX_CODEC_CORRUPT_FRAME;
hdr->frame_size_updated = 0;
if (hdr->is_keyframe)
{
unsigned int update = 0;
/* Keyframe header consists of a three-byte sync code
* followed by the width and height and associated scaling
* factors.
*/
if (data[3] != 0x9d || data[4] != 0x01 || data[5] != 0x2a)
return VPX_CODEC_UNSUP_BITSTREAM;
Bankoski, et al. Informational [Page 149]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
raw = data[6] | (data[7] << 8)
| (data[8] << 16) | (data[9] << 24);
CHECK_FOR_UPDATE(hdr->kf.w, BITS_GET(raw, 0, 14),
update);
CHECK_FOR_UPDATE(hdr->kf.scale_w, BITS_GET(raw, 14, 2),
update);
CHECK_FOR_UPDATE(hdr->kf.h, BITS_GET(raw, 16, 14),
update);
CHECK_FOR_UPDATE(hdr->kf.scale_h, BITS_GET(raw, 30, 2),
update);
hdr->frame_size_updated = update;
if (!hdr->kf.w || !hdr->kf.h)
return VPX_CODEC_UNSUP_BITSTREAM;
}
return VPX_CODEC_OK;
}
vpx_codec_err_t
vp8_dixie_decode_frame(struct vp8_decoder_ctx *ctx,
const unsigned char *data,
unsigned int sz)
{
volatile struct vp8_decoder_ctx *ctx_ = ctx;
ctx->error.error_code = VPX_CODEC_OK;
ctx->error.has_detail = 0;
if (!setjmp(ctx->error.jmp))
decode_frame(ctx, data, sz);
return ctx_->error.error_code;
}
void
vp8_dixie_decode_destroy(struct vp8_decoder_ctx *ctx)
{
vp8_dixie_predict_destroy(ctx);
vp8_dixie_tokens_destroy(ctx);
vp8_dixie_modemv_destroy(ctx);
}
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 150]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
20.5. dixie.h
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#ifndef DIXIE_H
#define DIXIE_H
#include "vpx_codec_internal.h"
#include "bool_decoder.h"
struct vp8_frame_hdr
{
unsigned int is_keyframe; /* Frame is a keyframe */
unsigned int is_experimental; /* Frame is a keyframe */
unsigned int version; /* Bitstream version */
unsigned int is_shown; /* Frame is to be displayed. */
unsigned int part0_sz; /* Partition 0 length, in bytes */
struct vp8_kf_hdr
{
unsigned int w; /* Width */
unsigned int h; /* Height */
unsigned int scale_w; /* Scaling factor, Width */
unsigned int scale_h; /* Scaling factor, Height */
} kf;
unsigned int frame_size_updated; /* Flag to indicate a resolution
* update.
*/
};
enum
{
MB_FEATURE_TREE_PROBS = 3,
MAX_MB_SEGMENTS = 4
};
Bankoski, et al. Informational [Page 151]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
struct vp8_segment_hdr
{
unsigned int enabled;
unsigned int update_data;
unsigned int update_map;
unsigned int abs; /* 0=deltas, 1=absolute values */
unsigned int tree_probs[MB_FEATURE_TREE_PROBS];
int lf_level[MAX_MB_SEGMENTS];
int quant_idx[MAX_MB_SEGMENTS];
};
enum
{
BLOCK_CONTEXTS = 4
};
struct vp8_loopfilter_hdr
{
unsigned int use_simple;
unsigned int level;
unsigned int sharpness;
unsigned int delta_enabled;
int ref_delta[BLOCK_CONTEXTS];
int mode_delta[BLOCK_CONTEXTS];
};
enum
{
MAX_PARTITIONS = 8
};
struct vp8_token_hdr
{
unsigned int partitions;
unsigned int partition_sz[MAX_PARTITIONS];
};
Bankoski, et al. Informational [Page 152]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
struct vp8_quant_hdr
{
unsigned int q_index;
int delta_update;
int y1_dc_delta_q;
int y2_dc_delta_q;
int y2_ac_delta_q;
int uv_dc_delta_q;
int uv_ac_delta_q;
};
struct vp8_reference_hdr
{
unsigned int refresh_last;
unsigned int refresh_gf;
unsigned int refresh_arf;
unsigned int copy_gf;
unsigned int copy_arf;
unsigned int sign_bias[4];
unsigned int refresh_entropy;
};
enum
{
BLOCK_TYPES = 4,
PREV_COEFF_CONTEXTS = 3,
COEFF_BANDS = 8,
ENTROPY_NODES = 11,
};
typedef unsigned char coeff_probs_table_t[BLOCK_TYPES][COEFF_BANDS]
[PREV_COEFF_CONTEXTS]
[ENTROPY_NODES];
enum
{
MV_PROB_CNT = 2 + 8 - 1 + 10 /* from entropymv.h */
};
typedef unsigned char mv_component_probs_t[MV_PROB_CNT];
Bankoski, et al. Informational [Page 153]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
struct vp8_entropy_hdr
{
coeff_probs_table_t coeff_probs;
mv_component_probs_t mv_probs[2];
unsigned int coeff_skip_enabled;
unsigned char coeff_skip_prob;
unsigned char y_mode_probs[4];
unsigned char uv_mode_probs[3];
unsigned char prob_inter;
unsigned char prob_last;
unsigned char prob_gf;
};
enum reference_frame
{
CURRENT_FRAME,
LAST_FRAME,
GOLDEN_FRAME,
ALTREF_FRAME,
NUM_REF_FRAMES
};
enum prediction_mode
{
/* 16x16 intra modes */
DC_PRED, V_PRED, H_PRED, TM_PRED, B_PRED,
/* 16x16 inter modes */
NEARESTMV, NEARMV, ZEROMV, NEWMV, SPLITMV,
MB_MODE_COUNT,
/* 4x4 intra modes */
B_DC_PRED = 0, B_TM_PRED, B_VE_PRED, B_HE_PRED, B_LD_PRED,
B_RD_PRED, B_VR_PRED, B_VL_PRED, B_HD_PRED, B_HU_PRED,
/* 4x4 inter modes */
LEFT4X4, ABOVE4X4, ZERO4X4, NEW4X4,
B_MODE_COUNT
};
Bankoski, et al. Informational [Page 154]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
enum splitmv_partitioning
{
SPLITMV_16X8,
SPLITMV_8X16,
SPLITMV_8X8,
SPLITMV_4X4
};
typedef short filter_t[6];
typedef union mv
{
struct
{
int16_t x, y;
} d;
uint32_t raw;
} mv_t;
struct mb_base_info
{
unsigned char y_mode : 4;
unsigned char uv_mode : 4;
unsigned char segment_id : 2;
unsigned char ref_frame : 2;
unsigned char skip_coeff : 1;
unsigned char need_mc_border : 1;
enum splitmv_partitioning partitioning : 2;
union mv mv;
unsigned int eob_mask;
};
struct mb_info
{
struct mb_base_info base;
union
{
union mv mvs[16];
enum prediction_mode modes[16];
} split;
};
Bankoski, et al. Informational [Page 155]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/* A "token entropy context" has 4 Y values, 2 U, 2 V, and 1 Y2 */
typedef int token_entropy_ctx_t[4 + 2 + 2 + 1];
struct token_decoder
{
struct bool_decoder bool;
token_entropy_ctx_t left_token_entropy_ctx;
short *coeffs;
};
enum token_block_type
{
TOKEN_BLOCK_Y1,
TOKEN_BLOCK_UV,
TOKEN_BLOCK_Y2,
TOKEN_BLOCK_TYPES,
};
struct dequant_factors
{
int quant_idx;
short factor[TOKEN_BLOCK_TYPES][2]; /* [ Y1, UV, Y2 ]
* [ DC, AC ] */
};
struct ref_cnt_img
{
vpx_image_t img;
unsigned int ref_cnt;
};
struct vp8_decoder_ctx
{
struct vpx_internal_error_info error;
unsigned int frame_cnt;
struct vp8_frame_hdr frame_hdr;
struct vp8_segment_hdr segment_hdr;
struct vp8_loopfilter_hdr loopfilter_hdr;
struct vp8_token_hdr token_hdr;
struct vp8_quant_hdr quant_hdr;
struct vp8_reference_hdr reference_hdr;
struct vp8_entropy_hdr entropy_hdr;
struct vp8_entropy_hdr saved_entropy;
unsigned int saved_entropy_valid;
Bankoski, et al. Informational [Page 156]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
unsigned int mb_rows;
unsigned int mb_cols;
struct mb_info *mb_info_storage;
struct mb_info **mb_info_rows_storage;
struct mb_info **mb_info_rows;
token_entropy_ctx_t *above_token_entropy_ctx;
struct token_decoder tokens[MAX_PARTITIONS];
struct dequant_factors dequant_factors[MAX_MB_SEGMENTS];
struct ref_cnt_img frame_strg[NUM_REF_FRAMES];
struct ref_cnt_img *ref_frames[NUM_REF_FRAMES];
ptrdiff_t ref_frame_offsets[4];
const filter_t *subpixel_filters;
};
void
vp8_dixie_decode_init(struct vp8_decoder_ctx *ctx);
void
vp8_dixie_decode_destroy(struct vp8_decoder_ctx *ctx);
vpx_codec_err_t
vp8_parse_frame_header(const unsigned char *data,
unsigned int sz,
struct vp8_frame_hdr *hdr);
vpx_codec_err_t
vp8_dixie_decode_frame(struct vp8_decoder_ctx *ctx,
const unsigned char *data,
unsigned int sz);
#define CLAMP_255(x) ((x)<0?0:((x)>255?255:(x)))
#endif
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 157]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
20.6. dixie_loopfilter.c
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#include "dixie.h"
#include "dixie_loopfilter.h"
#define ABS(x) ((x) >= 0 ? (x) : -(x))
#define p3 pixels[-4*stride]
#define p2 pixels[-3*stride]
#define p1 pixels[-2*stride]
#define p0 pixels[-1*stride]
#define q0 pixels[ 0*stride]
#define q1 pixels[ 1*stride]
#define q2 pixels[ 2*stride]
#define q3 pixels[ 3*stride]
#define static
static int
saturate_int8(int x)
{
if (x < -128)
return -128;
if (x > 127)
return 127;
return x;
}
Bankoski, et al. Informational [Page 158]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static int
saturate_uint8(int x)
{
if (x < 0)
return 0;
if (x > 255)
return 255;
return x;
}
static int
high_edge_variance(unsigned char *pixels,
int stride,
int hev_threshold)
{
return ABS(p1 - p0) > hev_threshold ||
ABS(q1 - q0) > hev_threshold;
}
static int
simple_threshold(unsigned char *pixels,
int stride,
int filter_limit)
{
return (ABS(p0 - q0) * 2 + (ABS(p1 - q1) >> 1)) <= filter_limit;
}
static int
normal_threshold(unsigned char *pixels,
int stride,
int edge_limit,
int interior_limit)
{
int E = edge_limit;
int I = interior_limit;
return simple_threshold(pixels, stride, 2 * E + I)
&& ABS(p3 - p2) <= I && ABS(p2 - p1) <= I
&& ABS(p1 - p0) <= I && ABS(q3 - q2) <= I
&& ABS(q2 - q1) <= I && ABS(q1 - q0) <= I;
}
Bankoski, et al. Informational [Page 159]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static void
filter_common(unsigned char *pixels,
int stride,
int use_outer_taps)
{
int a, f1, f2;
a = 3 * (q0 - p0);
if (use_outer_taps)
a += saturate_int8(p1 - q1);
a = saturate_int8(a);
f1 = ((a + 4 > 127) ? 127 : a + 4) >> 3;
f2 = ((a + 3 > 127) ? 127 : a + 3) >> 3;
p0 = saturate_uint8(p0 + f2);
q0 = saturate_uint8(q0 - f1);
if (!use_outer_taps)
{
/* This handles the case of subblock_filter()
* (from the bitstream guide.
*/
a = (f1 + 1) >> 1;
p1 = saturate_uint8(p1 + a);
q1 = saturate_uint8(q1 - a);
}
}
Bankoski, et al. Informational [Page 160]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static void
filter_mb_edge(unsigned char *pixels,
int stride)
{
int w, a;
w = saturate_int8(saturate_int8(p1 - q1) + 3 * (q0 - p0));
a = (27 * w + 63) >> 7;
p0 = saturate_uint8(p0 + a);
q0 = saturate_uint8(q0 - a);
a = (18 * w + 63) >> 7;
p1 = saturate_uint8(p1 + a);
q1 = saturate_uint8(q1 - a);
a = (9 * w + 63) >> 7;
p2 = saturate_uint8(p2 + a);
q2 = saturate_uint8(q2 - a);
}
static void
filter_mb_v_edge(unsigned char *src,
int stride,
int edge_limit,
int interior_limit,
int hev_threshold,
int size)
{
int i;
for (i = 0; i < 8 * size; i++)
{
if (normal_threshold(src, 1, edge_limit, interior_limit))
{
if (high_edge_variance(src, 1, hev_threshold))
filter_common(src, 1, 1);
else
filter_mb_edge(src, 1);
}
src += stride;
}
}
Bankoski, et al. Informational [Page 161]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static void
filter_subblock_v_edge(unsigned char *src,
int stride,
int edge_limit,
int interior_limit,
int hev_threshold,
int size)
{
int i;
for (i = 0; i < 8 * size; i++)
{
if (normal_threshold(src, 1, edge_limit, interior_limit))
filter_common(src, 1,
high_edge_variance(src, 1, hev_threshold));
src += stride;
}
}
static void
filter_mb_h_edge(unsigned char *src,
int stride,
int edge_limit,
int interior_limit,
int hev_threshold,
int size)
{
int i;
for (i = 0; i < 8 * size; i++)
{
if (normal_threshold(src, stride, edge_limit,
interior_limit))
{
if (high_edge_variance(src, stride, hev_threshold))
filter_common(src, stride, 1);
else
filter_mb_edge(src, stride);
}
src += 1;
}
}
Bankoski, et al. Informational [Page 162]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static void
filter_subblock_h_edge(unsigned char *src,
int stride,
int edge_limit,
int interior_limit,
int hev_threshold,
int size)
{
int i;
for (i = 0; i < 8 * size; i++)
{
if (normal_threshold(src, stride, edge_limit,
interior_limit))
filter_common(src, stride,
high_edge_variance(src, stride,
hev_threshold));
src += 1;
}
}
static void
filter_v_edge_simple(unsigned char *src,
int stride,
int filter_limit)
{
int i;
for (i = 0; i < 16; i++)
{
if (simple_threshold(src, 1, filter_limit))
filter_common(src, 1, 1);
src += stride;
}
}
Bankoski, et al. Informational [Page 163]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static void
filter_h_edge_simple(unsigned char *src,
int stride,
int filter_limit)
{
int i;
for (i = 0; i < 16; i++)
{
if (simple_threshold(src, stride, filter_limit))
filter_common(src, stride, 1);
src += 1;
}
}
static void
calculate_filter_parameters(struct vp8_decoder_ctx *ctx,
struct mb_info *mbi,
int *edge_limit_,
int *interior_limit_,
int *hev_threshold_)
{
int filter_level, interior_limit, hev_threshold;
/* Reference code/spec seems to conflate filter_level and
* edge_limit
*/
filter_level = ctx->loopfilter_hdr.level;
if (ctx->segment_hdr.enabled)
{
if (!ctx->segment_hdr.abs)
filter_level +=
ctx->segment_hdr.lf_level[mbi->base.segment_id];
else
filter_level =
ctx->segment_hdr.lf_level[mbi->base.segment_id];
}
if (filter_level > 63)
filter_level = 63;
else if (filter_level < 0)
filter_level = 0;
Bankoski, et al. Informational [Page 164]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
if (ctx->loopfilter_hdr.delta_enabled)
{
filter_level +=
ctx->loopfilter_hdr.ref_delta[mbi->base.ref_frame];
if (mbi->base.ref_frame == CURRENT_FRAME)
{
if (mbi->base.y_mode == B_PRED)
filter_level += ctx->loopfilter_hdr.mode_delta[0];
}
else if (mbi->base.y_mode == ZEROMV)
filter_level += ctx->loopfilter_hdr.mode_delta[1];
else if (mbi->base.y_mode == SPLITMV)
filter_level += ctx->loopfilter_hdr.mode_delta[3];
else
filter_level += ctx->loopfilter_hdr.mode_delta[2];
}
if (filter_level > 63)
filter_level = 63;
else if (filter_level < 0)
filter_level = 0;
interior_limit = filter_level;
if (ctx->loopfilter_hdr.sharpness)
{
interior_limit >>= ctx->loopfilter_hdr.sharpness > 4 ? 2 : 1;
if (interior_limit > 9 - ctx->loopfilter_hdr.sharpness)
interior_limit = 9 - ctx->loopfilter_hdr.sharpness;
}
if (interior_limit < 1)
interior_limit = 1;
hev_threshold = (filter_level >= 15);
if (filter_level >= 40)
hev_threshold++;
if (filter_level >= 20 && !ctx->frame_hdr.is_keyframe)
hev_threshold++;
*edge_limit_ = filter_level;
*interior_limit_ = interior_limit;
*hev_threshold_ = hev_threshold;
}
Bankoski, et al. Informational [Page 165]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static void
filter_row_normal(struct vp8_decoder_ctx *ctx,
unsigned int row,
unsigned int start_col,
unsigned int num_cols)
{
unsigned char *y, *u, *v;
int stride, uv_stride;
struct mb_info *mbi;
unsigned int col;
/* Adjust pointers based on row, start_col */
stride = ctx->ref_frames[CURRENT_FRAME]->img.stride[PLANE_Y];
uv_stride = ctx->ref_frames[CURRENT_FRAME]->img.stride[PLANE_U];
y = ctx->ref_frames[CURRENT_FRAME]->img.planes[PLANE_Y];
u = ctx->ref_frames[CURRENT_FRAME]->img.planes[PLANE_U];
v = ctx->ref_frames[CURRENT_FRAME]->img.planes[PLANE_V];
y += (stride * row + start_col) * 16;
u += (uv_stride * row + start_col) * 8;
v += (uv_stride * row + start_col) * 8;
mbi = ctx->mb_info_rows[row] + start_col;
for (col = start_col; col < start_col + num_cols; col++)
{
int edge_limit, interior_limit, hev_threshold;
/* TODO: Only need to recalculate every MB if segmentation is
* enabled.
*/
calculate_filter_parameters(ctx, mbi, &edge_limit,
&interior_limit, &hev_threshold);
if (edge_limit)
{
if (col)
{
filter_mb_v_edge(y, stride, edge_limit + 2,
interior_limit, hev_threshold, 2);
filter_mb_v_edge(u, uv_stride, edge_limit + 2,
interior_limit, hev_threshold, 1);
filter_mb_v_edge(v, uv_stride, edge_limit + 2,
interior_limit, hev_threshold, 1);
}
Bankoski, et al. Informational [Page 166]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/* NOTE: This conditional is actually dependent on the
* number of coefficients decoded, not the skip flag as
* coded in the bitstream. The tokens task is expected
* to set 31 if there is *any* non-zero data.
*/
if (mbi->base.eob_mask
|| mbi->base.y_mode == SPLITMV
|| mbi->base.y_mode == B_PRED)
{
filter_subblock_v_edge(y + 4, stride, edge_limit,
interior_limit, hev_threshold,
2);
filter_subblock_v_edge(y + 8, stride, edge_limit,
interior_limit, hev_threshold,
2);
filter_subblock_v_edge(y + 12, stride, edge_limit,
interior_limit, hev_threshold,
2);
filter_subblock_v_edge(u + 4, uv_stride, edge_limit,
interior_limit, hev_threshold,
1);
filter_subblock_v_edge(v + 4, uv_stride, edge_limit,
interior_limit, hev_threshold,
1);
}
if (row)
{
filter_mb_h_edge(y, stride, edge_limit + 2,
interior_limit, hev_threshold, 2);
filter_mb_h_edge(u, uv_stride, edge_limit + 2,
interior_limit, hev_threshold, 1);
filter_mb_h_edge(v, uv_stride, edge_limit + 2,
interior_limit, hev_threshold, 1);
}
Bankoski, et al. Informational [Page 167]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
if (mbi->base.eob_mask
|| mbi->base.y_mode == SPLITMV
|| mbi->base.y_mode == B_PRED)
{
filter_subblock_h_edge(y + 4 * stride, stride,
edge_limit, interior_limit,
hev_threshold, 2);
filter_subblock_h_edge(y + 8 * stride, stride,
edge_limit, interior_limit,
hev_threshold, 2);
filter_subblock_h_edge(y + 12 * stride, stride,
edge_limit, interior_limit,
hev_threshold, 2);
filter_subblock_h_edge(u + 4 * uv_stride, uv_stride,
edge_limit, interior_limit,
hev_threshold, 1);
filter_subblock_h_edge(v + 4 * uv_stride, uv_stride,
edge_limit, interior_limit,
hev_threshold, 1);
}
}
y += 16;
u += 8;
v += 8;
mbi++;
}
}
static void
filter_row_simple(struct vp8_decoder_ctx *ctx,
unsigned int row,
unsigned int start_col,
unsigned int num_cols)
{
unsigned char *y;
int stride;
struct mb_info *mbi;
unsigned int col;
/* Adjust pointers based on row, start_col */
stride = ctx->ref_frames[CURRENT_FRAME]->img.stride[PLANE_Y];
y = ctx->ref_frames[CURRENT_FRAME]->img.planes[PLANE_Y];
y += (stride * row + start_col) * 16;
mbi = ctx->mb_info_rows[row] + start_col;
Bankoski, et al. Informational [Page 168]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
for (col = start_col; col < start_col + num_cols; col++)
{
int edge_limit, interior_limit, hev_threshold;
/* TODO: Only need to recalculate every MB if segmentation is
* enabled.
*/
calculate_filter_parameters(ctx, mbi, &edge_limit,
&interior_limit, &hev_threshold);
if (edge_limit)
{
/* NOTE: This conditional is actually dependent on the
* number of coefficients decoded, not the skip flag as
* coded in the bitstream. The tokens task is expected
* to set 31 if there is *any* non-zero data.
*/
int filter_subblocks = (mbi->base.eob_mask
|| mbi->base.y_mode == SPLITMV
|| mbi->base.y_mode == B_PRED);
int mb_limit = (edge_limit + 2) * 2 + interior_limit;
int b_limit = edge_limit * 2 + interior_limit;
if (col)
filter_v_edge_simple(y, stride, mb_limit);
if (filter_subblocks)
{
filter_v_edge_simple(y + 4, stride, b_limit);
filter_v_edge_simple(y + 8, stride, b_limit);
filter_v_edge_simple(y + 12, stride, b_limit);
}
if (row)
filter_h_edge_simple(y, stride, mb_limit);
if (filter_subblocks)
{
filter_h_edge_simple(y + 4 * stride, stride,
b_limit);
filter_h_edge_simple(y + 8 * stride, stride,
b_limit);
filter_h_edge_simple(y + 12 * stride, stride,
b_limit);
}
}
Bankoski, et al. Informational [Page 169]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
y += 16;
mbi++;
}
}
void
vp8_dixie_loopfilter_process_row(struct vp8_decoder_ctx *ctx,
unsigned int row,
unsigned int start_col,
unsigned int num_cols)
{
if (ctx->loopfilter_hdr.use_simple)
filter_row_simple(ctx, row, start_col, num_cols);
else
filter_row_normal(ctx, row, start_col, num_cols);
}
---- End code block ----------------------------------------
20.7. dixie_loopfilter.h
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#ifndef DIXIE_LOOPFILTER_H
#define DIXIE_LOOPFILTER_H
void
vp8_dixie_loopfilter_process_row(struct vp8_decoder_ctx *ctx,
unsigned int row,
unsigned int start_col,
unsigned int num_cols);
#endif
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 170]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
20.8. idct_add.c
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#include "dixie.h"
#include "idct_add.h"
#include <assert.h>
void
vp8_dixie_walsh(const short *input, short *output)
{
int i;
int a1, b1, c1, d1;
int a2, b2, c2, d2;
const short *ip = input;
short *op = output;
for (i = 0; i < 4; i++)
{
a1 = ip[0] + ip[12];
b1 = ip[4] + ip[8];
c1 = ip[4] - ip[8];
d1 = ip[0] - ip[12];
op[0] = a1 + b1;
op[4] = c1 + d1;
op[8] = a1 - b1;
op[12] = d1 - c1;
ip++;
op++;
}
ip = output;
op = output;
Bankoski, et al. Informational [Page 171]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
for (i = 0; i < 4; i++)
{
a1 = ip[0] + ip[3];
b1 = ip[1] + ip[2];
c1 = ip[1] - ip[2];
d1 = ip[0] - ip[3];
a2 = a1 + b1;
b2 = c1 + d1;
c2 = a1 - b1;
d2 = d1 - c1;
op[0] = (a2 + 3) >> 3;
op[1] = (b2 + 3) >> 3;
op[2] = (c2 + 3) >> 3;
op[3] = (d2 + 3) >> 3;
ip += 4;
op += 4;
}
}
#define cospi8sqrt2minus1 20091
#define sinpi8sqrt2 35468
#define rounding 0
static void
idct_columns(const short *input, short *output)
{
int i;
int a1, b1, c1, d1;
const short *ip = input;
short *op = output;
int temp1, temp2;
int shortpitch = 4;
for (i = 0; i < 4; i++)
{
a1 = ip[0] + ip[8];
b1 = ip[0] - ip[8];
temp1 = (ip[4] * sinpi8sqrt2 + rounding) >> 16;
temp2 = ip[12] +
((ip[12] * cospi8sqrt2minus1 + rounding) >> 16);
c1 = temp1 - temp2;
Bankoski, et al. Informational [Page 172]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
temp1 = ip[4] +
((ip[4] * cospi8sqrt2minus1 + rounding) >> 16);
temp2 = (ip[12] * sinpi8sqrt2 + rounding) >> 16;
d1 = temp1 + temp2;
op[shortpitch*0] = a1 + d1;
op[shortpitch*3] = a1 - d1;
op[shortpitch*1] = b1 + c1;
op[shortpitch*2] = b1 - c1;
ip++;
op++;
}
}
void
vp8_dixie_idct_add(unsigned char *recon,
const unsigned char *predict,
int stride,
const short *coeffs)
{
int i;
int a1, b1, c1, d1, temp1, temp2;
short tmp[16];
idct_columns(coeffs, tmp);
coeffs = tmp;
for (i = 0; i < 4; i++)
{
a1 = coeffs[0] + coeffs[2];
b1 = coeffs[0] - coeffs[2];
temp1 = (coeffs[1] * sinpi8sqrt2 + rounding) >> 16;
temp2 = coeffs[3] +
((coeffs[3] * cospi8sqrt2minus1 + rounding) >> 16);
c1 = temp1 - temp2;
temp1 = coeffs[1] +
((coeffs[1] * cospi8sqrt2minus1 + rounding) >> 16);
temp2 = (coeffs[3] * sinpi8sqrt2 + rounding) >> 16;
d1 = temp1 + temp2;
recon[0] = CLAMP_255(predict[0] + ((a1 + d1 + 4) >> 3));
recon[3] = CLAMP_255(predict[3] + ((a1 - d1 + 4) >> 3));
recon[1] = CLAMP_255(predict[1] + ((b1 + c1 + 4) >> 3));
recon[2] = CLAMP_255(predict[2] + ((b1 - c1 + 4) >> 3));
Bankoski, et al. Informational [Page 173]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
coeffs += 4;
recon += stride;
predict += stride;
}
}
---- End code block ----------------------------------------
20.9. idct_add.h
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#ifndef IDCT_ADD_H
#define IDCT_ADD_H
void
vp8_dixie_idct_add_init(struct vp8_decoder_ctx *ctx);
void
vp8_dixie_idct_add(unsigned char *recon,
const unsigned char *predict,
int stride,
const short *coeffs);
void
vp8_dixie_walsh(const short *in, short *out);
void
vp8_dixie_idct_add_process_row(struct vp8_decoder_ctx *ctx,
short *coeffs,
unsigned int row,
unsigned int start_col,
unsigned int num_cols);
#endif
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 174]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
20.10. mem.h
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#ifndef VPX_PORTS_MEM_H
#define VPX_PORTS_MEM_H
#include "vpx_config.h"
#include "vpx_integer.h"
#if defined(__GNUC__) && __GNUC__
#define DECLARE_ALIGNED(n,typ,val) typ val __attribute__ \
((aligned (n)))
#elif defined(_MSC_VER)
#define DECLARE_ALIGNED(n,typ,val) __declspec(align(n)) typ val
#else
#warning No alignment directives known for this compiler.
#define DECLARE_ALIGNED(n,typ,val) typ val
#endif
#endif
/* Declare an aligned array on the stack, for situations where the
* stack pointer may not have the alignment we expect. Creates an
* array with a modified name, then defines val to be a pointer, and
* aligns that pointer within the array.
*/
#define DECLARE_ALIGNED_ARRAY(a,typ,val,n)\
typ val##_[(n)+(a)/sizeof(typ)+1];\
typ *val = (typ*)((((intptr_t)val##_)+(a)-1)&((intptr_t)-(a)))
Bankoski, et al. Informational [Page 175]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/* Indicates that the usage of the specified variable has been
* audited to assure that it's safe to use uninitialized. Silences
* 'may be used uninitialized' warnings on gcc.
*/
#if defined(__GNUC__) && __GNUC__
#define UNINITIALIZED_IS_SAFE(x) x=x
#else
#define UNINITIALIZED_IS_SAFE(x) x
#endif
---- End code block ----------------------------------------
20.11. modemv.c
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#include "dixie.h"
#include "modemv_data.h"
#include <stdlib.h>
#include <assert.h>
struct mv_clamp_rect
{
int to_left, to_right, to_top, to_bottom;
};
Bankoski, et al. Informational [Page 176]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static union mv
clamp_mv(union mv raw, const struct mv_clamp_rect *bounds)
{
union mv newmv;
newmv.d.x = (raw.d.x < bounds->to_left)
? bounds->to_left : raw.d.x;
newmv.d.x = (raw.d.x > bounds->to_right)
? bounds->to_right : newmv.d.x;
newmv.d.y = (raw.d.y < bounds->to_top)
? bounds->to_top : raw.d.y;
newmv.d.y = (raw.d.y > bounds->to_bottom)
? bounds->to_bottom : newmv.d.y;
return newmv;
}
static int
read_segment_id(struct bool_decoder *bool,
struct vp8_segment_hdr *seg)
{
return bool_get(bool, seg->tree_probs[0])
? 2 + bool_get(bool, seg->tree_probs[2])
: bool_get(bool, seg->tree_probs[1]);
}
static enum prediction_mode
above_block_mode(const struct mb_info *this,
const struct mb_info *above,
unsigned int b)
{
if (b < 4)
{
switch (above->base.y_mode)
{
case DC_PRED:
return B_DC_PRED;
case V_PRED:
return B_VE_PRED;
case H_PRED:
return B_HE_PRED;
Bankoski, et al. Informational [Page 177]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
case TM_PRED:
return B_TM_PRED;
case B_PRED:
return above->split.modes[b+12];
default:
assert(0);
}
}
return this->split.modes[b-4];
}
static enum prediction_mode
left_block_mode(const struct mb_info *this,
const struct mb_info *left,
unsigned int b)
{
if (!(b & 3))
{
switch (left->base.y_mode)
{
case DC_PRED:
return B_DC_PRED;
case V_PRED:
return B_VE_PRED;
case H_PRED:
return B_HE_PRED;
case TM_PRED:
return B_TM_PRED;
case B_PRED:
return left->split.modes[b+3];
default:
assert(0);
}
}
return this->split.modes[b-1];
}
Bankoski, et al. Informational [Page 178]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static void
decode_kf_mb_mode(struct mb_info *this,
struct mb_info *left,
struct mb_info *above,
struct bool_decoder *bool)
{
int y_mode, uv_mode;
y_mode = bool_read_tree(bool, kf_y_mode_tree, kf_y_mode_probs);
if (y_mode == B_PRED)
{
unsigned int i;
for (i = 0; i < 16; i++)
{
enum prediction_mode a = above_block_mode(this, above,
i);
enum prediction_mode l = left_block_mode(this, left, i);
enum prediction_mode b;
b = bool_read_tree(bool, b_mode_tree,
kf_b_mode_probs[a][l]);
this->split.modes[i] = b;
}
}
uv_mode = bool_read_tree(bool, uv_mode_tree, kf_uv_mode_probs);
this->base.y_mode = y_mode;
this->base.uv_mode = uv_mode;
this->base.mv.raw = 0;
this->base.ref_frame = 0;
}
static void
decode_intra_mb_mode(struct mb_info *this,
struct vp8_entropy_hdr *hdr,
struct bool_decoder *bool)
{
/* Like decode_kf_mb_mode, but with probabilities transmitted in
* the bitstream and no context on the above/left block mode.
*/
int y_mode, uv_mode;
y_mode = bool_read_tree(bool, y_mode_tree, hdr->y_mode_probs);
Bankoski, et al. Informational [Page 179]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
if (y_mode == B_PRED)
{
unsigned int i;
for (i = 0; i < 16; i++)
{
enum prediction_mode b;
b = bool_read_tree(bool, b_mode_tree,
default_b_mode_probs);
this->split.modes[i] = b;
}
}
uv_mode = bool_read_tree(bool, uv_mode_tree, hdr->uv_mode_probs);
this->base.y_mode = y_mode;
this->base.uv_mode = uv_mode;
this->base.mv.raw = 0;
this->base.ref_frame = CURRENT_FRAME;
}
static int
read_mv_component(struct bool_decoder *bool,
const unsigned char mvc[MV_PROB_CNT])
{
enum {IS_SHORT, SIGN, SHORT, BITS = SHORT + 8 - 1,
LONG_WIDTH = 10};
int x = 0;
if (bool_get(bool, mvc[IS_SHORT])) /* Large */
{
int i = 0;
for (i = 0; i < 3; i++)
x += bool_get(bool, mvc[BITS + i]) << i;
/* Skip bit 3, which is sometimes implicit */
for (i = LONG_WIDTH - 1; i > 3; i--)
x += bool_get(bool, mvc[BITS + i]) << i;
if (!(x & 0xFFF0) || bool_get(bool, mvc[BITS + 3]))
x += 8;
}
else /* small */
x = bool_read_tree(bool, small_mv_tree, mvc + SHORT);
Bankoski, et al. Informational [Page 180]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
if (x && bool_get(bool, mvc[SIGN]))
x = -x;
return x << 1;
}
static mv_t
above_block_mv(const struct mb_info *this,
const struct mb_info *above,
unsigned int b)
{
if (b < 4)
{
if (above->base.y_mode == SPLITMV)
return above->split.mvs[b+12];
return above->base.mv;
}
return this->split.mvs[b-4];
}
static mv_t
left_block_mv(const struct mb_info *this,
const struct mb_info *left,
unsigned int b)
{
if (!(b & 3))
{
if (left->base.y_mode == SPLITMV)
return left->split.mvs[b+3];
return left->base.mv;
}
return this->split.mvs[b-1];
}
Bankoski, et al. Informational [Page 181]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static enum prediction_mode
submv_ref(struct bool_decoder *bool, union mv l, union mv a)
{
enum subblock_mv_ref
{
SUBMVREF_NORMAL,
SUBMVREF_LEFT_ZED,
SUBMVREF_ABOVE_ZED,
SUBMVREF_LEFT_ABOVE_SAME,
SUBMVREF_LEFT_ABOVE_ZED
};
int lez = !(l.raw);
int aez = !(a.raw);
int lea = l.raw == a.raw;
enum subblock_mv_ref ctx = SUBMVREF_NORMAL;
if (lea && lez)
ctx = SUBMVREF_LEFT_ABOVE_ZED;
else if (lea)
ctx = SUBMVREF_LEFT_ABOVE_SAME;
else if (aez)
ctx = SUBMVREF_ABOVE_ZED;
else if (lez)
ctx = SUBMVREF_LEFT_ZED;
return bool_read_tree(bool, submv_ref_tree,
submv_ref_probs2[ctx]);
}
static void
read_mv(struct bool_decoder *bool,
union mv *mv,
mv_component_probs_t mvc[2])
{
mv->d.y = read_mv_component(bool, mvc[0]);
mv->d.x = read_mv_component(bool, mvc[1]);
}
Bankoski, et al. Informational [Page 182]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static void
mv_bias(const struct mb_info *mb,
const unsigned int sign_bias[3],
enum reference_frame ref_frame,
union mv *mv)
{
if (sign_bias[mb->base.ref_frame] ^ sign_bias[ref_frame])
{
mv->d.x *= -1;
mv->d.y *= -1;
}
}
enum near_mv_v
{
CNT_BEST = 0,
CNT_ZEROZERO = 0,
CNT_NEAREST,
CNT_NEAR,
CNT_SPLITMV
};
static void
find_near_mvs(const struct mb_info *this,
const struct mb_info *left,
const struct mb_info *above,
const unsigned int sign_bias[3],
union mv near_mvs[4],
int cnt[4])
{
const struct mb_info *aboveleft = above - 1;
union mv *mv = near_mvs;
int *cntx = cnt;
/* Zero accumulators */
mv[0].raw = mv[1].raw = mv[2].raw = 0;
cnt[0] = cnt[1] = cnt[2] = cnt[3] = 0;
Bankoski, et al. Informational [Page 183]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/* Process above */
if (above->base.ref_frame != CURRENT_FRAME)
{
if (above->base.mv.raw)
{
(++mv)->raw = above->base.mv.raw;
mv_bias(above, sign_bias, this->base.ref_frame, mv);
++cntx;
}
*cntx += 2;
}
/* Process left */
if (left->base.ref_frame != CURRENT_FRAME)
{
if (left->base.mv.raw)
{
union mv this_mv;
this_mv.raw = left->base.mv.raw;
mv_bias(left, sign_bias, this->base.ref_frame, &this_mv);
if (this_mv.raw != mv->raw)
{
(++mv)->raw = this_mv.raw;
++cntx;
}
*cntx += 2;
}
else
cnt[CNT_ZEROZERO] += 2;
}
/* Process above left */
if (aboveleft->base.ref_frame != CURRENT_FRAME)
{
if (aboveleft->base.mv.raw)
{
union mv this_mv;
this_mv.raw = aboveleft->base.mv.raw;
mv_bias(aboveleft, sign_bias, this->base.ref_frame,
&this_mv);
Bankoski, et al. Informational [Page 184]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
if (this_mv.raw != mv->raw)
{
(++mv)->raw = this_mv.raw;
++cntx;
}
*cntx += 1;
}
else
cnt[CNT_ZEROZERO] += 1;
}
/* If we have three distinct MVs ... */
if (cnt[CNT_SPLITMV])
{
/* See if above-left MV can be merged with NEAREST */
if (mv->raw == near_mvs[CNT_NEAREST].raw)
cnt[CNT_NEAREST] += 1;
}
cnt[CNT_SPLITMV] = ((above->base.y_mode == SPLITMV)
+ (left->base.y_mode == SPLITMV)) * 2
+ (aboveleft->base.y_mode == SPLITMV);
/* Swap near and nearest if necessary */
if (cnt[CNT_NEAR] > cnt[CNT_NEAREST])
{
int tmp;
tmp = cnt[CNT_NEAREST];
cnt[CNT_NEAREST] = cnt[CNT_NEAR];
cnt[CNT_NEAR] = tmp;
tmp = near_mvs[CNT_NEAREST].raw;
near_mvs[CNT_NEAREST].raw = near_mvs[CNT_NEAR].raw;
near_mvs[CNT_NEAR].raw = tmp;
}
/* Use near_mvs[CNT_BEST] to store the "best" MV. Note that this
* storage shares the same address as near_mvs[CNT_ZEROZERO].
*/
if (cnt[CNT_NEAREST] >= cnt[CNT_BEST])
near_mvs[CNT_BEST] = near_mvs[CNT_NEAREST];
}
Bankoski, et al. Informational [Page 185]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static void
decode_split_mv(struct mb_info *this,
const struct mb_info *left,
const struct mb_info *above,
struct vp8_entropy_hdr *hdr,
union mv *best_mv,
struct bool_decoder *bool)
{
const int *partition;
int j, k, mask, partition_id;
partition_id = bool_read_tree(bool, split_mv_tree,
split_mv_probs);
partition = mv_partitions[partition_id];
this->base.partitioning = partition_id;
for (j = 0, mask = 0; mask < 65535; j++)
{
union mv mv, left_mv, above_mv;
enum prediction_mode subblock_mode;
/* Find the first subblock in this partition. */
for (k = 0; j != partition[k]; k++);
/* Decode the next MV */
left_mv = left_block_mv(this, left, k);
above_mv = above_block_mv(this, above, k);
subblock_mode = submv_ref(bool, left_mv, above_mv);
switch (subblock_mode)
{
case LEFT4X4:
mv = left_mv;
break;
case ABOVE4X4:
mv = above_mv;
break;
case ZERO4X4:
mv.raw = 0;
break;
case NEW4X4:
read_mv(bool, &mv, hdr->mv_probs);
mv.d.x += best_mv->d.x;
mv.d.y += best_mv->d.y;
break;
default:
assert(0);
}
Bankoski, et al. Informational [Page 186]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/* Fill the MVs for this partition */
for (; k < 16; k++)
if (j == partition[k])
{
this->split.mvs[k] = mv;
mask |= 1 << k;
}
}
}
static int
need_mc_border(union mv mv, int l, int t, int b_w, int w, int h)
{
int b, r;
/* Get distance to edge for top-left pixel */
l += (mv.d.x >> 3);
t += (mv.d.y >> 3);
/* Get distance to edge for bottom-right pixel */
r = w - (l + b_w);
b = h - (t + b_w);
return (l >> 1 < 2 || r >> 1 < 3 || t >> 1 < 2 || b >> 1 < 3);
}
static void
decode_mvs(struct vp8_decoder_ctx *ctx,
struct mb_info *this,
const struct mb_info *left,
const struct mb_info *above,
const struct mv_clamp_rect *bounds,
struct bool_decoder *bool)
{
struct vp8_entropy_hdr *hdr = &ctx->entropy_hdr;
union mv near_mvs[4];
union mv clamped_best_mv;
int mv_cnts[4];
unsigned char probs[4];
enum {BEST, NEAREST, NEAR};
int x, y, w, h, b;
this->base.ref_frame = bool_get(bool, hdr->prob_last)
? 2 + bool_get(bool, hdr->prob_gf)
: 1;
Bankoski, et al. Informational [Page 187]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
find_near_mvs(this, this - 1, above,
ctx->reference_hdr.sign_bias, near_mvs, mv_cnts);
probs[0] = mv_counts_to_probs[mv_cnts[0]][0];
probs[1] = mv_counts_to_probs[mv_cnts[1]][1];
probs[2] = mv_counts_to_probs[mv_cnts[2]][2];
probs[3] = mv_counts_to_probs[mv_cnts[3]][3];
this->base.y_mode = bool_read_tree(bool, mv_ref_tree, probs);
this->base.uv_mode = this->base.y_mode;
this->base.need_mc_border = 0;
x = (-bounds->to_left - 128) >> 3;
y = (-bounds->to_top - 128) >> 3;
w = ctx->mb_cols * 16;
h = ctx->mb_rows * 16;
switch (this->base.y_mode)
{
case NEARESTMV:
this->base.mv = clamp_mv(near_mvs[NEAREST], bounds);
break;
case NEARMV:
this->base.mv = clamp_mv(near_mvs[NEAR], bounds);
break;
case ZEROMV:
this->base.mv.raw = 0;
return; //skip need_mc_border check
case NEWMV:
clamped_best_mv = clamp_mv(near_mvs[BEST], bounds);
read_mv(bool, &this->base.mv, hdr->mv_probs);
this->base.mv.d.x += clamped_best_mv.d.x;
this->base.mv.d.y += clamped_best_mv.d.y;
break;
case SPLITMV:
{
union mv chroma_mv[4] = {{{0}}};
clamped_best_mv = clamp_mv(near_mvs[BEST], bounds);
decode_split_mv(this, left, above, hdr, &clamped_best_mv,
bool);
this->base.mv = this->split.mvs[15];
Bankoski, et al. Informational [Page 188]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
for (b = 0; b < 16; b++)
{
chroma_mv[(b>>1&1) + (b>>2&2)].d.x +=
this->split.mvs[b].d.x;
chroma_mv[(b>>1&1) + (b>>2&2)].d.y +=
this->split.mvs[b].d.y;
if (need_mc_border(this->split.mvs[b],
x + (b & 3) * 4, y + (b & ~3), 4, w, h))
{
this->base.need_mc_border = 1;
break;
}
}
for (b = 0; b < 4; b++)
{
chroma_mv[b].d.x += 4 + 8 * (chroma_mv[b].d.x >> 31);
chroma_mv[b].d.y += 4 + 8 * (chroma_mv[b].d.y >> 31);
chroma_mv[b].d.x /= 4;
chroma_mv[b].d.y /= 4;
//note we're passing in non-subsampled coordinates
if (need_mc_border(chroma_mv[b],
x + (b & 1) * 8, y + (b >> 1) * 8, 16, w, h))
{
this->base.need_mc_border = 1;
break;
}
}
return; //skip need_mc_border check
}
default:
assert(0);
}
if (need_mc_border(this->base.mv, x, y, 16, w, h))
this->base.need_mc_border = 1;
}
Bankoski, et al. Informational [Page 189]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
void
vp8_dixie_modemv_process_row(struct vp8_decoder_ctx *ctx,
struct bool_decoder *bool,
int row,
int start_col,
int num_cols)
{
struct mb_info *above, *this;
unsigned int col;
struct mv_clamp_rect bounds;
this = ctx->mb_info_rows[row] + start_col;
above = ctx->mb_info_rows[row - 1] + start_col;
/* Calculate the eighth-pel MV bounds using a 1 MB border. */
bounds.to_left = -((start_col + 1) << 7);
bounds.to_right = (ctx->mb_cols - start_col) << 7;
bounds.to_top = -((row + 1) << 7);
bounds.to_bottom = (ctx->mb_rows - row) << 7;
for (col = start_col; col < start_col + num_cols; col++)
{
if (ctx->segment_hdr.update_map)
this->base.segment_id = read_segment_id(bool,
&ctx->segment_hdr);
if (ctx->entropy_hdr.coeff_skip_enabled)
this->base.skip_coeff = bool_get(bool,
ctx->entropy_hdr.coeff_skip_prob);
if (ctx->frame_hdr.is_keyframe)
{
if (!ctx->segment_hdr.update_map)
this->base.segment_id = 0;
decode_kf_mb_mode(this, this - 1, above, bool);
}
else
{
if (bool_get(bool, ctx->entropy_hdr.prob_inter))
decode_mvs(ctx, this, this - 1, above, &bounds,
bool);
else
decode_intra_mb_mode(this, &ctx->entropy_hdr, bool);
bounds.to_left -= 16 << 3;
bounds.to_right -= 16 << 3;
}
Bankoski, et al. Informational [Page 190]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/* Advance to next mb */
this++;
above++;
}
}
void
vp8_dixie_modemv_init(struct vp8_decoder_ctx *ctx)
{
unsigned int mbi_w, mbi_h, i;
struct mb_info *mbi;
mbi_w = ctx->mb_cols + 1; /* For left border col */
mbi_h = ctx->mb_rows + 1; /* For above border row */
if (ctx->frame_hdr.frame_size_updated)
{
free(ctx->mb_info_storage);
ctx->mb_info_storage = NULL;
free(ctx->mb_info_rows_storage);
ctx->mb_info_rows_storage = NULL;
}
if (!ctx->mb_info_storage)
ctx->mb_info_storage = calloc(mbi_w * mbi_h,
sizeof(*ctx->mb_info_storage));
if (!ctx->mb_info_rows_storage)
ctx->mb_info_rows_storage = calloc(mbi_h,
sizeof(*ctx->mb_info_rows_storage));
/* Set up row pointers */
mbi = ctx->mb_info_storage + 1;
for (i = 0; i < mbi_h; i++)
{
ctx->mb_info_rows_storage[i] = mbi;
mbi += mbi_w;
}
ctx->mb_info_rows = ctx->mb_info_rows_storage + 1;
}
Bankoski, et al. Informational [Page 191]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
void
vp8_dixie_modemv_destroy(struct vp8_decoder_ctx *ctx)
{
free(ctx->mb_info_storage);
ctx->mb_info_storage = NULL;
free(ctx->mb_info_rows_storage);
ctx->mb_info_rows_storage = NULL;
}
---- End code block ----------------------------------------
20.12. modemv.h
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#ifndef MODEMV_H
#define MODEMV_H
void
vp8_dixie_modemv_init(struct vp8_decoder_ctx *ctx);
void
vp8_dixie_modemv_destroy(struct vp8_decoder_ctx *ctx);
void
vp8_dixie_modemv_process_row(struct vp8_decoder_ctx *ctx,
struct bool_decoder *bool,
int row,
int start_col,
int num_cols);
#endif
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 192]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
20.13. modemv_data.h
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
static const unsigned char kf_y_mode_probs[] = { 145, 156, 163, 128};
static const unsigned char kf_uv_mode_probs[] = { 142, 114, 183};
static const unsigned char kf_b_mode_probs[10][10][9] =
{
{ /* above mode 0 */
{ /* left mode 0 */ 231, 120, 48, 89, 115, 113, 120, 152, 112},
{ /* left mode 1 */ 152, 179, 64, 126, 170, 118, 46, 70, 95},
{ /* left mode 2 */ 175, 69, 143, 80, 85, 82, 72, 155, 103},
{ /* left mode 3 */ 56, 58, 10, 171, 218, 189, 17, 13, 152},
{ /* left mode 4 */ 144, 71, 10, 38, 171, 213, 144, 34, 26},
{ /* left mode 5 */ 114, 26, 17, 163, 44, 195, 21, 10, 173},
{ /* left mode 6 */ 121, 24, 80, 195, 26, 62, 44, 64, 85},
{ /* left mode 7 */ 170, 46, 55, 19, 136, 160, 33, 206, 71},
{ /* left mode 8 */ 63, 20, 8, 114, 114, 208, 12, 9, 226},
{ /* left mode 9 */ 81, 40, 11, 96, 182, 84, 29, 16, 36}
},
{ /* above mode 1 */
{ /* left mode 0 */ 134, 183, 89, 137, 98, 101, 106, 165, 148},
{ /* left mode 1 */ 72, 187, 100, 130, 157, 111, 32, 75, 80},
{ /* left mode 2 */ 66, 102, 167, 99, 74, 62, 40, 234, 128},
{ /* left mode 3 */ 41, 53, 9, 178, 241, 141, 26, 8, 107},
{ /* left mode 4 */ 104, 79, 12, 27, 217, 255, 87, 17, 7},
{ /* left mode 5 */ 74, 43, 26, 146, 73, 166, 49, 23, 157},
{ /* left mode 6 */ 65, 38, 105, 160, 51, 52, 31, 115, 128},
{ /* left mode 7 */ 87, 68, 71, 44, 114, 51, 15, 186, 23},
{ /* left mode 8 */ 47, 41, 14, 110, 182, 183, 21, 17, 194},
{ /* left mode 9 */ 66, 45, 25, 102, 197, 189, 23, 18, 22}
},
{ /* above mode 2 */
{ /* left mode 0 */ 88, 88, 147, 150, 42, 46, 45, 196, 205},
{ /* left mode 1 */ 43, 97, 183, 117, 85, 38, 35, 179, 61},
{ /* left mode 2 */ 39, 53, 200, 87, 26, 21, 43, 232, 171},
{ /* left mode 3 */ 56, 34, 51, 104, 114, 102, 29, 93, 77},
{ /* left mode 4 */ 107, 54, 32, 26, 51, 1, 81, 43, 31},
Bankoski, et al. Informational [Page 193]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{ /* left mode 5 */ 39, 28, 85, 171, 58, 165, 90, 98, 64},
{ /* left mode 6 */ 34, 22, 116, 206, 23, 34, 43, 166, 73},
{ /* left mode 7 */ 68, 25, 106, 22, 64, 171, 36, 225, 114},
{ /* left mode 8 */ 34, 19, 21, 102, 132, 188, 16, 76, 124},
{ /* left mode 9 */ 62, 18, 78, 95, 85, 57, 50, 48, 51}
},
{ /* above mode 3 */
{ /* left mode 0 */ 193, 101, 35, 159, 215, 111, 89, 46, 111},
{ /* left mode 1 */ 60, 148, 31, 172, 219, 228, 21, 18, 111},
{ /* left mode 2 */ 112, 113, 77, 85, 179, 255, 38, 120, 114},
{ /* left mode 3 */ 40, 42, 1, 196, 245, 209, 10, 25, 109},
{ /* left mode 4 */ 100, 80, 8, 43, 154, 1, 51, 26, 71},
{ /* left mode 5 */ 88, 43, 29, 140, 166, 213, 37, 43, 154},
{ /* left mode 6 */ 61, 63, 30, 155, 67, 45, 68, 1, 209},
{ /* left mode 7 */ 142, 78, 78, 16, 255, 128, 34, 197, 171},
{ /* left mode 8 */ 41, 40, 5, 102, 211, 183, 4, 1, 221},
{ /* left mode 9 */ 51, 50, 17, 168, 209, 192, 23, 25, 82}
},
{ /* above mode 4 */
{ /* left mode 0 */ 125, 98, 42, 88, 104, 85, 117, 175, 82},
{ /* left mode 1 */ 95, 84, 53, 89, 128, 100, 113, 101, 45},
{ /* left mode 2 */ 75, 79, 123, 47, 51, 128, 81, 171, 1},
{ /* left mode 3 */ 57, 17, 5, 71, 102, 57, 53, 41, 49},
{ /* left mode 4 */ 115, 21, 2, 10, 102, 255, 166, 23, 6},
{ /* left mode 5 */ 38, 33, 13, 121, 57, 73, 26, 1, 85},
{ /* left mode 6 */ 41, 10, 67, 138, 77, 110, 90, 47, 114},
{ /* left mode 7 */ 101, 29, 16, 10, 85, 128, 101, 196, 26},
{ /* left mode 8 */ 57, 18, 10, 102, 102, 213, 34, 20, 43},
{ /* left mode 9 */ 117, 20, 15, 36, 163, 128, 68, 1, 26}
},
{ /* above mode 5 */
{ /* left mode 0 */ 138, 31, 36, 171, 27, 166, 38, 44, 229},
{ /* left mode 1 */ 67, 87, 58, 169, 82, 115, 26, 59, 179},
{ /* left mode 2 */ 63, 59, 90, 180, 59, 166, 93, 73, 154},
{ /* left mode 3 */ 40, 40, 21, 116, 143, 209, 34, 39, 175},
{ /* left mode 4 */ 57, 46, 22, 24, 128, 1, 54, 17, 37},
{ /* left mode 5 */ 47, 15, 16, 183, 34, 223, 49, 45, 183},
{ /* left mode 6 */ 46, 17, 33, 183, 6, 98, 15, 32, 183},
{ /* left mode 7 */ 65, 32, 73, 115, 28, 128, 23, 128, 205},
{ /* left mode 8 */ 40, 3, 9, 115, 51, 192, 18, 6, 223},
{ /* left mode 9 */ 87, 37, 9, 115, 59, 77, 64, 21, 47}
},
{ /* above mode 6 */
{ /* left mode 0 */ 104, 55, 44, 218, 9, 54, 53, 130, 226},
{ /* left mode 1 */ 64, 90, 70, 205, 40, 41, 23, 26, 57},
{ /* left mode 2 */ 54, 57, 112, 184, 5, 41, 38, 166, 213},
{ /* left mode 3 */ 30, 34, 26, 133, 152, 116, 10, 32, 134},
{ /* left mode 4 */ 75, 32, 12, 51, 192, 255, 160, 43, 51},
Bankoski, et al. Informational [Page 194]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{ /* left mode 5 */ 39, 19, 53, 221, 26, 114, 32, 73, 255},
{ /* left mode 6 */ 31, 9, 65, 234, 2, 15, 1, 118, 73},
{ /* left mode 7 */ 88, 31, 35, 67, 102, 85, 55, 186, 85},
{ /* left mode 8 */ 56, 21, 23, 111, 59, 205, 45, 37, 192},
{ /* left mode 9 */ 55, 38, 70, 124, 73, 102, 1, 34, 98}
},
{ /* above mode 7 */
{ /* left mode 0 */ 102, 61, 71, 37, 34, 53, 31, 243, 192},
{ /* left mode 1 */ 69, 60, 71, 38, 73, 119, 28, 222, 37},
{ /* left mode 2 */ 68, 45, 128, 34, 1, 47, 11, 245, 171},
{ /* left mode 3 */ 62, 17, 19, 70, 146, 85, 55, 62, 70},
{ /* left mode 4 */ 75, 15, 9, 9, 64, 255, 184, 119, 16},
{ /* left mode 5 */ 37, 43, 37, 154, 100, 163, 85, 160, 1},
{ /* left mode 6 */ 63, 9, 92, 136, 28, 64, 32, 201, 85},
{ /* left mode 7 */ 86, 6, 28, 5, 64, 255, 25, 248, 1},
{ /* left mode 8 */ 56, 8, 17, 132, 137, 255, 55, 116, 128},
{ /* left mode 9 */ 58, 15, 20, 82, 135, 57, 26, 121, 40}
},
{ /* above mode 8 */
{ /* left mode 0 */ 164, 50, 31, 137, 154, 133, 25, 35, 218},
{ /* left mode 1 */ 51, 103, 44, 131, 131, 123, 31, 6, 158},
{ /* left mode 2 */ 86, 40, 64, 135, 148, 224, 45, 183, 128},
{ /* left mode 3 */ 22, 26, 17, 131, 240, 154, 14, 1, 209},
{ /* left mode 4 */ 83, 12, 13, 54, 192, 255, 68, 47, 28},
{ /* left mode 5 */ 45, 16, 21, 91, 64, 222, 7, 1, 197},
{ /* left mode 6 */ 56, 21, 39, 155, 60, 138, 23, 102, 213},
{ /* left mode 7 */ 85, 26, 85, 85, 128, 128, 32, 146, 171},
{ /* left mode 8 */ 18, 11, 7, 63, 144, 171, 4, 4, 246},
{ /* left mode 9 */ 35, 27, 10, 146, 174, 171, 12, 26, 128}
},
{ /* above mode 9 */
{ /* left mode 0 */ 190, 80, 35, 99, 180, 80, 126, 54, 45},
{ /* left mode 1 */ 85, 126, 47, 87, 176, 51, 41, 20, 32},
{ /* left mode 2 */ 101, 75, 128, 139, 118, 146, 116, 128, 85},
{ /* left mode 3 */ 56, 41, 15, 176, 236, 85, 37, 9, 62},
{ /* left mode 4 */ 146, 36, 19, 30, 171, 255, 97, 27, 20},
{ /* left mode 5 */ 71, 30, 17, 119, 118, 255, 17, 18, 138},
{ /* left mode 6 */ 101, 38, 60, 138, 55, 70, 43, 26, 142},
{ /* left mode 7 */ 138, 45, 61, 62, 219, 1, 81, 188, 64},
{ /* left mode 8 */ 32, 41, 20, 117, 151, 142, 20, 21, 163},
{ /* left mode 9 */ 112, 19, 12, 61, 195, 128, 48, 4, 24}
}
};
Bankoski, et al. Informational [Page 195]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static const int kf_y_mode_tree[] =
{
-B_PRED, 2,
4, 6,
-DC_PRED, -V_PRED,
-H_PRED, -TM_PRED
};
static const int y_mode_tree[] =
{
-DC_PRED, 2,
4, 6,
-V_PRED, -H_PRED,
-TM_PRED, -B_PRED
};
static const int uv_mode_tree[6] =
{
-DC_PRED, 2,
-V_PRED, 4,
-H_PRED, -TM_PRED
};
static const int b_mode_tree[18] =
{
-B_DC_PRED, 2, /* 0 = DC_NODE */
-B_TM_PRED, 4, /* 1 = TM_NODE */
-B_VE_PRED, 6, /* 2 = VE_NODE */
8, 12, /* 3 = COM_NODE */
-B_HE_PRED, 10, /* 4 = HE_NODE */
-B_RD_PRED, -B_VR_PRED, /* 5 = RD_NODE */
-B_LD_PRED, 14, /* 6 = LD_NODE */
-B_VL_PRED, 16, /* 7 = VL_NODE */
-B_HD_PRED, -B_HU_PRED /* 8 = HD_NODE */
};
static const int small_mv_tree[14] =
{
2, 8,
4, 6,
-0, -1,
-2, -3,
10, 12,
-4, -5,
-6, -7
};
Bankoski, et al. Informational [Page 196]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static const int mv_ref_tree[8] =
{
-ZEROMV, 2,
-NEARESTMV, 4,
-NEARMV, 6,
-NEWMV, -SPLITMV
};
static const int submv_ref_tree[6] =
{
-LEFT4X4, 2,
-ABOVE4X4, 4,
-ZERO4X4, -NEW4X4
};
static const int split_mv_tree[6] =
{
-3, 2,
-2, 4,
-0, -1
};
static const unsigned char default_b_mode_probs[] =
{ 120, 90, 79, 133, 87, 85, 80, 111, 151};
static const unsigned char mv_counts_to_probs[6][4] =
{
{ 7, 1, 1, 143 },
{ 14, 18, 14, 107 },
{ 135, 64, 57, 68 },
{ 60, 56, 128, 65 },
{ 159, 134, 128, 34 },
{ 234, 188, 128, 28 }
};
static const unsigned char split_mv_probs[3] =
{ 110, 111, 150};
static const unsigned char submv_ref_probs2[5][3] =
{
{ 147, 136, 18 },
{ 106, 145, 1 },
{ 179, 121, 1 },
{ 223, 1, 34 },
{ 208, 1, 1 }
};
Bankoski, et al. Informational [Page 197]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
const static int mv_partitions[4][16] =
{
{0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1 },
{0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1, 0, 0, 1, 1 },
{0, 0, 1, 1, 0, 0, 1, 1, 2, 2, 3, 3, 2, 2, 3, 3 },
{0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 }
};
---- End code block ----------------------------------------
20.14. predict.c
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#include "dixie.h"
#include "predict.h"
#include "idct_add.h"
#include "mem.h"
#include <assert.h>
#include <string.h>
enum
{
BORDER_PIXELS = 16,
};
static const filter_t sixtap_filters[8] =
{
{ 0, 0, 128, 0, 0, 0 },
{ 0, -6, 123, 12, -1, 0 },
{ 2, -11, 108, 36, -8, 1 },
{ 0, -9, 93, 50, -6, 0 },
{ 3, -16, 77, 77, -16, 3 },
{ 0, -6, 50, 93, -9, 0 },
{ 1, -8, 36, 108, -11, 2 },
{ 0, -1, 12, 123, -6, 0 }
};
Bankoski, et al. Informational [Page 198]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static const filter_t bilinear_filters[8] =
{
{ 0, 0, 128, 0, 0, 0 },
{ 0, 0, 112, 16, 0, 0 },
{ 0, 0, 96, 32, 0, 0 },
{ 0, 0, 80, 48, 0, 0 },
{ 0, 0, 64, 64, 0, 0 },
{ 0, 0, 48, 80, 0, 0 },
{ 0, 0, 32, 96, 0, 0 },
{ 0, 0, 16, 112, 0, 0 }
};
static void
predict_h_nxn(unsigned char *predict,
int stride,
int n)
{
unsigned char *left = predict - 1;
int i, j;
for (i = 0; i < n; i++)
for (j = 0; j < n; j++)
predict[i *stride + j] = left[i * stride];
}
static void
predict_v_nxn(unsigned char *predict,
int stride,
int n)
{
unsigned char *above = predict - stride;
int i, j;
for (i = 0; i < n; i++)
for (j = 0; j < n; j++)
predict[i *stride + j] = above[j];
}
Bankoski, et al. Informational [Page 199]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static void
predict_tm_nxn(unsigned char *predict,
int stride,
int n)
{
/* Transposes the left column to the top row for later
* consumption by the idct/recon stage
*/
unsigned char *left = predict - 1;
unsigned char *above = predict - stride;
unsigned char p = above[-1];
int i, j;
for (j = 0; j < n; j++)
{
for (i = 0; i < n; i++)
predict[i] = CLAMP_255(*left + above[i] - p);
predict += stride;
left += stride;
}
}
static void
predict_dc_nxn(unsigned char *predict,
int stride,
int n)
{
unsigned char *left = predict - 1;
unsigned char *above = predict - stride;
int i, j, dc = 0;
for (i = 0; i < n; i++)
{
dc += *left + above[i];
left += stride;
}
Bankoski, et al. Informational [Page 200]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
switch (n)
{
case 16:
dc = (dc + 16) >> 5;
break;
case 8:
dc = (dc + 8) >> 4;
break;
case 4:
dc = (dc + 4) >> 3;
break;
}
for (i = 0; i < n; i++)
for (j = 0; j < n; j++)
predict[i *stride + j] = dc;
}
static void
predict_ve_4x4(unsigned char *predict,
int stride)
{
unsigned char *above = predict - stride;
int i, j;
predict[0] = (above[-1] + 2 * above[0] + above[1] + 2) >> 2;
predict[1] = (above[ 0] + 2 * above[1] + above[2] + 2) >> 2;
predict[2] = (above[ 1] + 2 * above[2] + above[3] + 2) >> 2;
predict[3] = (above[ 2] + 2 * above[3] + above[4] + 2) >> 2;
for (i = 1; i < 4; i++)
for (j = 0; j < 4; j++)
predict[i *stride + j] = predict[j];
}
Bankoski, et al. Informational [Page 201]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static void
predict_he_4x4(unsigned char *predict,
int stride)
{
unsigned char *left = predict - 1;
predict[0] =
predict[1] =
predict[2] =
predict[3] = (left[-stride] + 2 * left[0] +
left[stride] + 2) >> 2;
predict += stride;
left += stride;
predict[0] =
predict[1] =
predict[2] =
predict[3] = (left[-stride] + 2 * left[0] +
left[stride] + 2) >> 2;
predict += stride;
left += stride;
predict[0] =
predict[1] =
predict[2] =
predict[3] = (left[-stride] + 2 * left[0] +
left[stride] + 2) >> 2;
predict += stride;
left += stride;
predict[0] =
predict[1] =
predict[2] =
predict[3] = (left[-stride] + 2 * left[0] + left[0] + 2) >> 2;
}
Bankoski, et al. Informational [Page 202]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static void
predict_ld_4x4(unsigned char *predict,
int stride)
{
unsigned char *above = predict - stride;
int pred0, pred1, pred2, pred3, pred4, pred5, pred6;
predict[0] = pred0 = (above[0] + 2 * above[1] +
above[2] + 2) >> 2;
predict[1] = pred1 = (above[1] + 2 * above[2] +
above[3] + 2) >> 2;
predict[2] = pred2 = (above[2] + 2 * above[3] +
above[4] + 2) >> 2;
predict[3] = pred3 = (above[3] + 2 * above[4] +
above[5] + 2) >> 2;
predict += stride;
predict[0] = pred1;
predict[1] = pred2;
predict[2] = pred3;
predict[3] = pred4 = (above[4] + 2 * above[5] +
above[6] + 2) >> 2;
predict += stride;
predict[0] = pred2;
predict[1] = pred3;
predict[2] = pred4;
predict[3] = pred5 = (above[5] + 2 * above[6] +
above[7] + 2) >> 2;
predict += stride;
predict[0] = pred3;
predict[1] = pred4;
predict[2] = pred5;
predict[3] = pred6 = (above[6] + 2 * above[7] +
above[7] + 2) >> 2;
}
Bankoski, et al. Informational [Page 203]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static void
predict_rd_4x4(unsigned char *predict,
int stride)
{
unsigned char *left = predict - 1;
unsigned char *above = predict - stride;
int pred0, pred1, pred2, pred3, pred4, pred5, pred6;
predict[0] = pred0 =
(left[ 0] + 2 * above[-1] + above[0] + 2) >> 2;
predict[1] = pred1 =
(above[-1] + 2 * above[ 0] + above[1] + 2) >> 2;
predict[2] = pred2 =
(above[ 0] + 2 * above[ 1] + above[2] + 2) >> 2;
predict[3] = pred3 =
(above[ 1] + 2 * above[ 2] + above[3] + 2) >> 2;
predict += stride;
predict[0] = pred4 =
(left[stride] + 2 * left[0] + above[-1] + 2) >> 2;
predict[1] = pred0;
predict[2] = pred1;
predict[3] = pred2;
predict += stride;
predict[0] = pred5 =
(left[stride*2] + 2 * left[stride] + left[0] + 2) >> 2;
predict[1] = pred4;
predict[2] = pred0;
predict[3] = pred1;
predict += stride;
predict[0] = pred6 = (left[stride*3] + 2 * left[stride*2] +
left[stride] + 2) >> 2;
predict[1] = pred5;
predict[2] = pred4;
predict[3] = pred0;
}
Bankoski, et al. Informational [Page 204]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static void
predict_vr_4x4(unsigned char *predict,
int stride)
{
unsigned char *left = predict - 1;
unsigned char *above = predict - stride;
int pred0, pred1, pred2, pred3, pred4, pred5, pred6,
pred7, pred8, pred9;
predict[0] = pred0 = (above[-1] + above[0] + 1) >> 1;
predict[1] = pred1 = (above[ 0] + above[1] + 1) >> 1;
predict[2] = pred2 = (above[ 1] + above[2] + 1) >> 1;
predict[3] = pred3 = (above[ 2] + above[3] + 1) >> 1;
predict += stride;
predict[0] = pred4 = (left[ 0] + 2 * above[-1] +
above[0] + 2) >> 2;
predict[1] = pred5 = (above[-1] + 2 * above[ 0] +
above[1] + 2) >> 2;
predict[2] = pred6 = (above[ 0] + 2 * above[ 1] +
above[2] + 2) >> 2;
predict[3] = pred7 = (above[ 1] + 2 * above[ 2] +
above[3] + 2) >> 2;
predict += stride;
predict[0] = pred8 =
(left[stride] + 2 * left[0] + above[-1] + 2) >> 2;
predict[1] = pred0;
predict[2] = pred1;
predict[3] = pred2;
predict += stride;
predict[0] = pred9 =
(left[stride*2] + 2 * left[stride] + left[0] + 2) >> 2;
predict[1] = pred4;
predict[2] = pred5;
predict[3] = pred6;
}
Bankoski, et al. Informational [Page 205]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static void
predict_vl_4x4(unsigned char *predict,
int stride)
{
unsigned char *above = predict - stride;
int pred0, pred1, pred2, pred3, pred4, pred5, pred6,
pred7, pred8, pred9;
predict[0] = pred0 = (above[0] + above[1] + 1) >> 1;
predict[1] = pred1 = (above[1] + above[2] + 1) >> 1;
predict[2] = pred2 = (above[2] + above[3] + 1) >> 1;
predict[3] = pred3 = (above[3] + above[4] + 1) >> 1;
predict += stride;
predict[0] = pred4 = (above[0] + 2 * above[1] +
above[2] + 2) >> 2;
predict[1] = pred5 = (above[1] + 2 * above[2] +
above[3] + 2) >> 2;
predict[2] = pred6 = (above[2] + 2 * above[3] +
above[4] + 2) >> 2;
predict[3] = pred7 = (above[3] + 2 * above[4] +
above[5] + 2) >> 2;
predict += stride;
predict[0] = pred1;
predict[1] = pred2;
predict[2] = pred3;
predict[3] = pred8 = (above[4] + 2 * above[5] +
above[6] + 2) >> 2;
predict += stride;
predict[0] = pred5;
predict[1] = pred6;
predict[2] = pred7;
predict[3] = pred9 = (above[5] + 2 * above[6] +
above[7] + 2) >> 2;
}
Bankoski, et al. Informational [Page 206]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static void
predict_hd_4x4(unsigned char *predict,
int stride)
{
unsigned char *left = predict - 1;
unsigned char *above = predict - stride;
int pred0, pred1, pred2, pred3, pred4, pred5, pred6,
pred7, pred8, pred9;
predict[0] = pred0 = (left[ 0] + above[-1] + 1) >> 1;
predict[1] = pred1 = (left[ 0] + 2 * above[-1] +
above[0] + 2) >> 2;
predict[2] = pred2 = (above[-1] + 2 * above[ 0] +
above[1] + 2) >> 2;
predict[3] = pred3 = (above[ 0] + 2 * above[ 1] +
above[2] + 2) >> 2;
predict += stride;
predict[0] = pred4 = (left[stride] + left[0] + 1) >> 1;
predict[1] = pred5 = (left[stride] + 2 * left[0] +
above[-1] + 2) >> 2;
predict[2] = pred0;
predict[3] = pred1;
predict += stride;
predict[0] = pred6 = (left[stride*2] + left[stride] + 1) >> 1;
predict[1] = pred7 = (left[stride*2] + 2 * left[stride] +
left[0] + 2) >> 2;
predict[2] = pred4;
predict[3] = pred5;
predict += stride;
predict[0] = pred8 = (left[stride*3] + left[stride*2] + 1) >> 1;
predict[1] = pred9 = (left[stride*3] + 2 * left[stride*2] +
left[stride] + 2) >> 2;
predict[2] = pred6;
predict[3] = pred7;
}
Bankoski, et al. Informational [Page 207]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static void
predict_hu_4x4(unsigned char *predict,
int stride)
{
unsigned char *left = predict - 1;
int pred0, pred1, pred2, pred3, pred4, pred5, pred6;
predict[0] = pred0 = (left[stride*0] +
left[stride*1] + 1) >> 1;
predict[1] = pred1 = (left[stride*0] + 2 * left[stride*1] +
left[stride*2] + 2) >> 2;
predict[2] = pred2 = (left[stride*1] + left[stride*2] + 1) >> 1;
predict[3] = pred3 = (left[stride*1] + 2 * left[stride*2] +
left[stride*3] + 2) >> 2;
predict += stride;
predict[0] = pred2;
predict[1] = pred3;
predict[2] = pred4 = (left[stride*2] + left[stride*3] + 1) >> 1;
predict[3] = pred5 = (left[stride*2] + 2 * left[stride*3] +
left[stride*3] + 2) >> 2;
predict += stride;
predict[0] = pred4;
predict[1] = pred5;
predict[2] = pred6 = left[stride*3];
predict[3] = pred6;
predict += stride;
predict[0] = pred6;
predict[1] = pred6;
predict[2] = pred6;
predict[3] = pred6;
}
static void
predict_h_16x16(unsigned char *predict, int stride)
{
predict_h_nxn(predict, stride, 16);
}
static void
predict_v_16x16(unsigned char *predict, int stride)
{
predict_v_nxn(predict, stride, 16);
}
Bankoski, et al. Informational [Page 208]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static void
predict_tm_16x16(unsigned char *predict, int stride)
{
predict_tm_nxn(predict, stride, 16);
}
static void
predict_h_8x8(unsigned char *predict, int stride)
{
predict_h_nxn(predict, stride, 8);
}
static void
predict_v_8x8(unsigned char *predict, int stride)
{
predict_v_nxn(predict, stride, 8);
}
static void
predict_tm_8x8(unsigned char *predict, int stride)
{
predict_tm_nxn(predict, stride, 8);
}
static void
predict_tm_4x4(unsigned char *predict, int stride)
{
predict_tm_nxn(predict, stride, 4);
}
static void
copy_down(unsigned char *recon,
int stride)
{
/* Copy the four pixels above-right of subblock 3 to
* above-right of subblocks 7, 11, and 15
*/
uint32_t tmp, *copy = (void *)(recon + 16 - stride);
Bankoski, et al. Informational [Page 209]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
stride = stride / sizeof(unsigned int);
tmp = *copy;
copy += stride * 4;
*copy = tmp;
copy += stride * 4;
*copy = tmp;
copy += stride * 4;
*copy = tmp;
}
static void
b_pred(unsigned char *predict,
int stride,
struct mb_info *mbi,
short *coeffs)
{
int i;
copy_down(predict, stride);
for (i = 0; i < 16; i++)
{
unsigned char *b_predict = predict + (i & 3) * 4;
switch (mbi->split.modes[i])
{
case B_DC_PRED:
predict_dc_nxn(b_predict, stride, 4);
break;
case B_TM_PRED:
predict_tm_4x4(b_predict, stride);
break;
case B_VE_PRED:
predict_ve_4x4(b_predict, stride);
break;
case B_HE_PRED:
predict_he_4x4(b_predict, stride);
break;
case B_LD_PRED:
predict_ld_4x4(b_predict, stride);
break;
case B_RD_PRED:
predict_rd_4x4(b_predict, stride);
break;
case B_VR_PRED:
predict_vr_4x4(b_predict, stride);
break;
Bankoski, et al. Informational [Page 210]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
case B_VL_PRED:
predict_vl_4x4(b_predict, stride);
break;
case B_HD_PRED:
predict_hd_4x4(b_predict, stride);
break;
case B_HU_PRED:
predict_hu_4x4(b_predict, stride);
break;
default:
assert(0);
}
vp8_dixie_idct_add(b_predict, b_predict, stride, coeffs);
coeffs += 16;
if ((i & 3) == 3)
{
predict += stride * 4;
}
}
}
static void
fixup_dc_coeffs(struct mb_info *mbi,
short *coeffs)
{
short y2[16];
int i;
vp8_dixie_walsh(coeffs + 24 * 16, y2);
for (i = 0; i < 16; i++)
coeffs[i*16] = y2[i];
}
static void
predict_intra_luma(unsigned char *predict,
int stride,
struct mb_info *mbi,
short *coeffs)
{
if (mbi->base.y_mode == B_PRED)
b_pred(predict, stride, mbi, coeffs);
else
Bankoski, et al. Informational [Page 211]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{
int i;
switch (mbi->base.y_mode)
{
case DC_PRED:
predict_dc_nxn(predict, stride, 16);
break;
case V_PRED:
predict_v_16x16(predict, stride);
break;
case H_PRED:
predict_h_16x16(predict, stride);
break;
case TM_PRED:
predict_tm_16x16(predict, stride);
break;
default:
assert(0);
}
fixup_dc_coeffs(mbi, coeffs);
for (i = 0; i < 16; i++)
{
vp8_dixie_idct_add(predict, predict, stride, coeffs);
coeffs += 16;
predict += 4;
if ((i & 3) == 3)
predict += stride * 4 - 16;
}
}
}
static void
predict_intra_chroma(unsigned char *predict_u,
unsigned char *predict_v,
int stride,
struct mb_info *mbi,
short *coeffs)
{
int i;
Bankoski, et al. Informational [Page 212]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
switch (mbi->base.uv_mode)
{
case DC_PRED:
predict_dc_nxn(predict_u, stride, 8);
predict_dc_nxn(predict_v, stride, 8);
break;
case V_PRED:
predict_v_8x8(predict_u, stride);
predict_v_8x8(predict_v, stride);
break;
case H_PRED:
predict_h_8x8(predict_u, stride);
predict_h_8x8(predict_v, stride);
break;
case TM_PRED:
predict_tm_8x8(predict_u, stride);
predict_tm_8x8(predict_v, stride);
break;
default:
assert(0);
}
coeffs += 16 * 16;
for (i = 16; i < 20; i++)
{
vp8_dixie_idct_add(predict_u, predict_u, stride, coeffs);
coeffs += 16;
predict_u += 4;
if (i & 1)
predict_u += stride * 4 - 8;
}
for (i = 20; i < 24; i++)
{
vp8_dixie_idct_add(predict_v, predict_v, stride, coeffs);
coeffs += 16;
predict_v += 4;
if (i & 1)
predict_v += stride * 4 - 8;
}
}
Bankoski, et al. Informational [Page 213]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static void
sixtap_horiz(unsigned char *output,
int output_stride,
const unsigned char *reference,
int reference_stride,
int cols,
int rows,
const filter_t filter
)
{
int r, c, temp;
for (r = 0; r < rows; r++)
{
for (c = 0; c < cols; c++)
{
temp = (reference[-2] * filter[0]) +
(reference[-1] * filter[1]) +
(reference[ 0] * filter[2]) +
(reference[ 1] * filter[3]) +
(reference[ 2] * filter[4]) +
(reference[ 3] * filter[5]) +
64;
temp >>= 7;
output[c] = CLAMP_255(temp);
reference++;
}
reference += reference_stride - cols;
output += output_stride;
}
}
static void
sixtap_vert(unsigned char *output,
int output_stride,
const unsigned char *reference,
int reference_stride,
int cols,
int rows,
const filter_t filter
)
{
int r, c, temp;
for (r = 0; r < rows; r++)
{
Bankoski, et al. Informational [Page 214]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
for (c = 0; c < cols; c++)
{
temp = (reference[-2*reference_stride] * filter[0]) +
(reference[-1*reference_stride] * filter[1]) +
(reference[ 0*reference_stride] * filter[2]) +
(reference[ 1*reference_stride] * filter[3]) +
(reference[ 2*reference_stride] * filter[4]) +
(reference[ 3*reference_stride] * filter[5]) +
64;
temp >>= 7;
output[c] = CLAMP_255(temp);
reference++;
}
reference += reference_stride - cols;
output += output_stride;
}
}
static void
sixtap_2d(unsigned char *output,
int output_stride,
const unsigned char *reference,
int reference_stride,
int cols,
int rows,
int mx,
int my,
const filter_t filters[8]
)
{
DECLARE_ALIGNED(16, unsigned char, temp[16*(16+5)]);
sixtap_horiz(temp, 16,
reference - 2 * reference_stride, reference_stride,
cols, rows + 5, filters[mx]);
sixtap_vert(output, output_stride,
temp + 2 * 16, 16,
cols, rows, filters[my]);
}
struct img_index
{
unsigned char *y, *u, *v;
int stride, uv_stride;
};
Bankoski, et al. Informational [Page 215]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static const unsigned char *
filter_block(unsigned char *output,
const unsigned char *reference,
int stride,
const union mv *mv,
const filter_t filters[8])
{
int mx, my;
/* Handle 0,0 as a special case. TODO: Does this make it any
* faster?
*/
if (!mv->raw)
return reference;
mx = mv->d.x & 7;
my = mv->d.y & 7;
reference += ((mv->d.y >> 3) * stride) + (mv->d.x >> 3);
if (mx | my)
{
sixtap_2d(output, stride, reference, stride, 4, 4, mx, my,
filters);
reference = output;
}
return reference;
}
static void
recon_1_block(unsigned char *output,
const unsigned char *reference,
int stride,
const union mv *mv,
const filter_t filters[8],
short *coeffs,
struct mb_info *mbi,
int b
)
{
const unsigned char *predict;
predict = filter_block(output, reference, stride, mv, filters);
vp8_dixie_idct_add(output, predict, stride, coeffs + 16 * b);
}
Bankoski, et al. Informational [Page 216]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static mv_t
calculate_chroma_splitmv(struct mb_info *mbi,
int b,
int full_pixel)
{
int temp;
union mv mv;
temp = mbi->split.mvs[b].d.x +
mbi->split.mvs[b+1].d.x +
mbi->split.mvs[b+4].d.x +
mbi->split.mvs[b+5].d.x;
if (temp < 0)
temp -= 4;
else
temp += 4;
mv.d.x = temp / 8;
temp = mbi->split.mvs[b].d.y +
mbi->split.mvs[b+1].d.y +
mbi->split.mvs[b+4].d.y +
mbi->split.mvs[b+5].d.y;
if (temp < 0)
temp -= 4;
else
temp += 4;
mv.d.y = temp / 8;
if (full_pixel)
{
mv.d.x &= ~7;
mv.d.y &= ~7;
}
return mv;
}
Bankoski, et al. Informational [Page 217]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/* Note: We rely on the reconstructed border having the same stride
* as the reference buffer because the filter_block can't adjust the
* stride with its return value, only the reference pointer.
*/
static void
build_mc_border(unsigned char *dst,
const unsigned char *src,
int stride,
int x,
int y,
int b_w,
int b_h,
int w,
int h
)
{
const unsigned char *ref_row;
/* Get a pointer to the start of the real data for this row */
ref_row = src - x - y * stride;
if (y >= h)
ref_row += (h - 1) * stride;
else if (y > 0)
ref_row += y * stride;
do
{
int left, right = 0, copy;
left = x < 0 ? -x : 0;
if (left > b_w)
left = b_w;
if (x + b_w > w)
right = x + b_w - w;
if (right > b_w)
right = b_w;
Bankoski, et al. Informational [Page 218]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
copy = b_w - left - right;
if (left)
memset(dst, ref_row[0], left);
if (copy)
memcpy(dst + left, ref_row + x + left, copy);
if (right)
memset(dst + left + copy, ref_row[w-1], right);
dst += stride;
y++;
if (y < h && y > 0)
ref_row += stride;
}
while (--b_h);
}
static void
recon_1_edge_block(unsigned char *output,
unsigned char *emul_block,
const unsigned char *reference,
int stride,
const union mv *mv,
const filter_t filters[8],
short *coeffs,
struct mb_info *mbi,
int x,
int y,
int w,
int h,
int start_b
)
{
const unsigned char *predict;
int b = start_b;
const int b_w = 4;
const int b_h = 4;
x += mv->d.x >> 3;
y += mv->d.y >> 3;
Bankoski, et al. Informational [Page 219]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/* Need two pixels left/above, 3 right/below for 6-tap */
if (x < 2 || x + b_w - 1 + 3 >= w || y < 2 ||
y + b_h - 1 + 3 >= h)
{
reference += (mv->d.x >> 3) + (mv->d.y >> 3) * stride;
build_mc_border(emul_block,
reference - 2 - 2 * stride, stride,
x - 2, y - 2, b_w + 5, b_h + 5, w, h);
reference = emul_block + 2 * stride + 2;
reference -= (mv->d.x >> 3) + (mv->d.y >> 3) * stride;
}
predict = filter_block(output, reference, stride, mv, filters);
vp8_dixie_idct_add(output, predict, stride, coeffs + 16 * b);
}
static void
predict_inter_emulated_edge(struct vp8_decoder_ctx *ctx,
struct img_index *img,
short *coeffs,
struct mb_info *mbi,
int mb_col,
int mb_row)
{
/* TODO: Move this into its own buffer. This only works because
* we still have a border allocated.
*/
unsigned char *emul_block = ctx->frame_strg[0].img.img_data;
unsigned char *reference;
unsigned char *output;
ptrdiff_t reference_offset;
int w, h, x, y, b;
union mv chroma_mv[4];
unsigned char *u = img->u, *v = img->v;
int full_pixel = ctx->frame_hdr.version == 3;
x = mb_col * 16;
y = mb_row * 16;
w = ctx->mb_cols * 16;
h = ctx->mb_rows * 16;
output = img->y;
reference_offset = ctx->ref_frame_offsets[mbi->base.ref_frame];
reference = output + reference_offset;
Bankoski, et al. Informational [Page 220]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
if (mbi->base.y_mode != SPLITMV)
{
union mv uvmv;
uvmv = mbi->base.mv;
uvmv.d.x = (uvmv.d.x + 1 + (uvmv.d.x >> 31) * 2) / 2;
uvmv.d.y = (uvmv.d.y + 1 + (uvmv.d.y >> 31) * 2) / 2;
if (full_pixel)
{
uvmv.d.x &= ~7;
uvmv.d.y &= ~7;
}
chroma_mv[0] = uvmv;
chroma_mv[1] = uvmv;
chroma_mv[2] = uvmv;
chroma_mv[3] = uvmv;
}
else
{
chroma_mv[0] = calculate_chroma_splitmv(mbi, 0, full_pixel);
chroma_mv[1] = calculate_chroma_splitmv(mbi, 2, full_pixel);
chroma_mv[2] = calculate_chroma_splitmv(mbi, 8, full_pixel);
chroma_mv[3] = calculate_chroma_splitmv(mbi, 10, full_pixel);
}
/* Luma */
for (b = 0; b < 16; b++)
{
union mv *ymv;
if (mbi->base.y_mode != SPLITMV)
ymv = &mbi->base.mv;
else
ymv = mbi->split.mvs + b;
recon_1_edge_block(output, emul_block, reference,
img->stride, ymv, ctx->subpixel_filters, coeffs,
mbi, x, y, w, h, b);
x += 4;
output += 4;
reference += 4;
Bankoski, et al. Informational [Page 221]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
if ((b & 3) == 3)
{
x -= 16;
y += 4;
output += 4 * img->stride - 16;
reference += 4 * img->stride - 16;
}
}
x = mb_col * 16;
y = mb_row * 16;
/* Chroma */
x >>= 1;
y >>= 1;
w >>= 1;
h >>= 1;
for (b = 0; b < 4; b++)
{
recon_1_edge_block(u, emul_block, u + reference_offset,
img->uv_stride,
&chroma_mv[b], ctx->subpixel_filters,
coeffs, mbi, x, y, w, h, b + 16);
recon_1_edge_block(v, emul_block, v + reference_offset,
img->uv_stride,
&chroma_mv[b], ctx->subpixel_filters,
coeffs, mbi, x, y, w, h, b + 20);
u += 4;
v += 4;
x += 4;
if (b & 1)
{
x -= 8;
y += 4;
u += 4 * img->uv_stride - 8;
v += 4 * img->uv_stride - 8;
}
}
}
static void
predict_inter(struct vp8_decoder_ctx *ctx,
struct img_index *img,
short *coeffs,
struct mb_info *mbi)
Bankoski, et al. Informational [Page 222]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{
unsigned char *y = img->y;
unsigned char *u = img->u;
unsigned char *v = img->v;
ptrdiff_t reference_offset;
union mv chroma_mv[4];
int full_pixel = ctx->frame_hdr.version == 3;
int b;
if (mbi->base.y_mode != SPLITMV)
{
union mv uvmv;
uvmv = mbi->base.mv;
uvmv.d.x = (uvmv.d.x + 1 + (uvmv.d.x >> 31) * 2) / 2;
uvmv.d.y = (uvmv.d.y + 1 + (uvmv.d.y >> 31) * 2) / 2;
if (full_pixel)
{
uvmv.d.x &= ~7;
uvmv.d.y &= ~7;
}
chroma_mv[0] =
chroma_mv[1] =
chroma_mv[2] =
chroma_mv[3] = uvmv;
}
else
{
chroma_mv[0] = calculate_chroma_splitmv(mbi, 0, full_pixel);
chroma_mv[1] = calculate_chroma_splitmv(mbi, 2, full_pixel);
chroma_mv[2] = calculate_chroma_splitmv(mbi, 8, full_pixel);
chroma_mv[3] = calculate_chroma_splitmv(mbi, 10, full_pixel);
}
reference_offset = ctx->ref_frame_offsets[mbi->base.ref_frame];
for (b = 0; b < 16; b++)
{
union mv *ymv;
if (mbi->base.y_mode != SPLITMV)
ymv = &mbi->base.mv;
else
ymv = mbi->split.mvs + b;
recon_1_block(y, y + reference_offset, img->stride,
ymv, ctx->subpixel_filters, coeffs, mbi, b);
Bankoski, et al. Informational [Page 223]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
y += 4;
if ((b & 3) == 3)
y += 4 * img->stride - 16;
}
for (b = 0; b < 4; b++)
{
recon_1_block(u, u + reference_offset,
img->uv_stride, &chroma_mv[b],
ctx->subpixel_filters, coeffs, mbi, b + 16);
recon_1_block(v, v + reference_offset,
img->uv_stride, &chroma_mv[b],
ctx->subpixel_filters, coeffs, mbi, b + 20);
u += 4;
v += 4;
if (b & 1)
{
u += 4 * img->uv_stride - 8;
v += 4 * img->uv_stride - 8;
}
}
}
void
vp8_dixie_release_ref_frame(struct ref_cnt_img *rcimg)
{
if (rcimg)
{
assert(rcimg->ref_cnt);
rcimg->ref_cnt--;
}
}
struct ref_cnt_img *
vp8_dixie_ref_frame(struct ref_cnt_img *rcimg)
{
rcimg->ref_cnt++;
return rcimg;
}
Bankoski, et al. Informational [Page 224]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
struct ref_cnt_img *
vp8_dixie_find_free_ref_frame(struct ref_cnt_img *frames)
{
int i;
for (i = 0; i < NUM_REF_FRAMES; i++)
if (frames[i].ref_cnt == 0)
{
frames[i].ref_cnt = 1;
return &frames[i];
}
assert(0);
return NULL;
}
static void
fixup_left(unsigned char *predict,
int width,
int stride,
unsigned int row,
enum prediction_mode mode)
{
/* The left column of out-of-frame pixels is taken to be 129,
* unless we're doing DC_PRED, in which case we duplicate the
* above row, unless this is also row 0, in which case we use
* 129.
*/
unsigned char *left = predict - 1;
int i;
if (mode == DC_PRED && row)
{
unsigned char *above = predict - stride;
for (i = 0; i < width; i++)
{
*left = above[i];
left += stride;
}
}
else
{
/* Need to re-set the above row, in case the above MB was
* DC_PRED.
*/
left -= stride;
Bankoski, et al. Informational [Page 225]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
for (i = -1; i < width; i++)
{
*left = 129;
left += stride;
}
}
}
static void
fixup_above(unsigned char *predict,
int width,
int stride,
unsigned int col,
enum prediction_mode mode)
{
/* The above row of out-of-frame pixels is taken to be 127,
* unless we're doing DC_PRED, in which case we duplicate the
* left col, unless this is also col 0, in which case we use
* 127.
*/
unsigned char *above = predict - stride;
int i;
if (mode == DC_PRED && col)
{
unsigned char *left = predict - 1;
for (i = 0; i < width; i++)
{
above[i] = *left;
left += stride;
}
}
else
/* Need to re-set the left col, in case the last MB was
* DC_PRED.
*/
memset(above - 1, 127, width + 1);
memset(above + width, 127, 4); // for above-right subblock modes
}
Bankoski, et al. Informational [Page 226]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
void
vp8_dixie_predict_init(struct vp8_decoder_ctx *ctx)
{
int i;
unsigned char *this_frame_base;
if (ctx->frame_hdr.frame_size_updated)
{
for (i = 0; i < NUM_REF_FRAMES; i++)
{
unsigned int w = ctx->mb_cols * 16 + BORDER_PIXELS * 2;
unsigned int h = ctx->mb_rows * 16 + BORDER_PIXELS * 2;
vpx_img_free(&ctx->frame_strg[i].img);
ctx->frame_strg[i].ref_cnt = 0;
ctx->ref_frames[i] = NULL;
if (!vpx_img_alloc(&ctx->frame_strg[i].img,
IMG_FMT_I420, w, h, 16))
vpx_internal_error(&ctx->error, VPX_CODEC_MEM_ERROR,
"Failed to allocate %dx%d"
" framebuffer",
w, h);
vpx_img_set_rect(&ctx->frame_strg[i].img, BORDER_PIXELS,
BORDER_PIXELS, ctx->frame_hdr.kf.w,
ctx->frame_hdr.kf.h);
}
if (ctx->frame_hdr.version)
ctx->subpixel_filters = bilinear_filters;
else
ctx->subpixel_filters = sixtap_filters;
}
/* Find a free framebuffer to predict into */
if (ctx->ref_frames[CURRENT_FRAME])
vp8_dixie_release_ref_frame(ctx->ref_frames[CURRENT_FRAME]);
ctx->ref_frames[CURRENT_FRAME] =
vp8_dixie_find_free_ref_frame(ctx->frame_strg);
this_frame_base = ctx->ref_frames[CURRENT_FRAME]->img.img_data;
Bankoski, et al. Informational [Page 227]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/* Calculate offsets to the other reference frames */
for (i = 0; i < NUM_REF_FRAMES; i++)
{
struct ref_cnt_img *ref = ctx->ref_frames[i];
ctx->ref_frame_offsets[i] =
ref ? ref->img.img_data - this_frame_base : 0;
}
/* TODO: No need to do this on every frame... */
}
void
vp8_dixie_predict_destroy(struct vp8_decoder_ctx *ctx)
{
int i;
for (i = 0; i < NUM_REF_FRAMES; i++)
{
vpx_img_free(&ctx->frame_strg[i].img);
ctx->frame_strg[i].ref_cnt = 0;
ctx->ref_frames[i] = NULL;
}
}
void
vp8_dixie_predict_process_row(struct vp8_decoder_ctx *ctx,
unsigned int row,
unsigned int start_col,
unsigned int num_cols)
{
struct img_index img;
struct mb_info *mbi;
unsigned int col;
short *coeffs;
Bankoski, et al. Informational [Page 228]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/* Adjust pointers based on row, start_col */
img.stride =
ctx->ref_frames[CURRENT_FRAME]->img.stride[PLANE_Y];
img.uv_stride =
ctx->ref_frames[CURRENT_FRAME]->img.stride[PLANE_U];
img.y = ctx->ref_frames[CURRENT_FRAME]->img.planes[PLANE_Y];
img.u = ctx->ref_frames[CURRENT_FRAME]->img.planes[PLANE_U];
img.v = ctx->ref_frames[CURRENT_FRAME]->img.planes[PLANE_V];
img.y += (img.stride * row + start_col) * 16;
img.u += (img.uv_stride * row + start_col) * 8;
img.v += (img.uv_stride * row + start_col) * 8;
mbi = ctx->mb_info_rows[row] + start_col;
coeffs = ctx->tokens[row &
(ctx->token_hdr.partitions - 1)].coeffs +
25 * 16 * start_col;
/* Fix up the out-of-frame pixels */
if (start_col == 0)
{
fixup_left(img.y, 16, img.stride, row, mbi->base.y_mode);
fixup_left(img.u, 8, img.uv_stride, row, mbi->base.uv_mode);
fixup_left(img.v, 8, img.uv_stride, row, mbi->base.uv_mode);
if (row == 0)
*(img.y - img.stride - 1) = 127;
}
for (col = start_col; col < start_col + num_cols; col++)
{
if (row == 0)
{
fixup_above(img.y, 16, img.stride, col,
mbi->base.y_mode);
fixup_above(img.u, 8, img.uv_stride, col,
mbi->base.uv_mode);
fixup_above(img.v, 8, img.uv_stride, col,
mbi->base.uv_mode);
}
if (mbi->base.y_mode <= B_PRED)
{
predict_intra_luma(img.y, img.stride, mbi, coeffs);
predict_intra_chroma(img.u, img.v, img.uv_stride, mbi,
coeffs);
}
Bankoski, et al. Informational [Page 229]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
else
{
if (mbi->base.y_mode != SPLITMV) // && != BPRED
fixup_dc_coeffs(mbi, coeffs);
if (mbi->base.need_mc_border)
predict_inter_emulated_edge(ctx, &img, coeffs, mbi,
col, row);
else
predict_inter(ctx, &img, coeffs, mbi);
}
/* Advance to the next macroblock */
mbi++;
img.y += 16;
img.u += 8;
img.v += 8;
coeffs += 25 * 16;
}
if (col == ctx->mb_cols)
{
/* Extend the last row by four pixels for intra-prediction.
* This will be propagated later by copy_down.
*/
uint32_t *extend = (uint32_t *)(img.y + 15 * img.stride);
uint32_t val = 0x01010101 * img.y[-1 + 15 * img.stride];
*extend = val;
}
}
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 230]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
20.15. predict.h
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#ifndef PREDICT_H
#define PREDICT_H
void
vp8_dixie_predict_init(struct vp8_decoder_ctx *ctx);
void
vp8_dixie_predict_destroy(struct vp8_decoder_ctx *ctx);
void
vp8_dixie_predict_process_row(struct vp8_decoder_ctx *ctx,
unsigned int row,
unsigned int start_col,
unsigned int num_cols);
void
vp8_dixie_release_ref_frame(struct ref_cnt_img *rcimg);
struct ref_cnt_img *
vp8_dixie_ref_frame(struct ref_cnt_img *rcimg);
struct ref_cnt_img *
vp8_dixie_find_free_ref_frame(struct ref_cnt_img *frames);
#endif
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 231]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
20.16. tokens.c
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#include "vpx_codec_internal.h"
#include "dixie.h"
#include "tokens.h"
#include <stdlib.h>
#include <string.h>
#include <malloc.h>
enum
{
EOB_CONTEXT_NODE,
ZERO_CONTEXT_NODE,
ONE_CONTEXT_NODE,
LOW_VAL_CONTEXT_NODE,
TWO_CONTEXT_NODE,
THREE_CONTEXT_NODE,
HIGH_LOW_CONTEXT_NODE,
CAT_ONE_CONTEXT_NODE,
CAT_THREEFOUR_CONTEXT_NODE,
CAT_THREE_CONTEXT_NODE,
CAT_FIVE_CONTEXT_NODE
};
enum
{
ZERO_TOKEN,
ONE_TOKEN,
TWO_TOKEN,
THREE_TOKEN,
FOUR_TOKEN,
DCT_VAL_CATEGORY1,
DCT_VAL_CATEGORY2,
DCT_VAL_CATEGORY3,
Bankoski, et al. Informational [Page 232]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
DCT_VAL_CATEGORY4,
DCT_VAL_CATEGORY5,
DCT_VAL_CATEGORY6,
DCT_EOB_TOKEN,
MAX_ENTROPY_TOKENS
};
struct extrabits
{
short min_val;
short length;
unsigned char probs[12];
};
static const unsigned int left_context_index[25] =
{
0, 0, 0, 0, 1, 1, 1, 1, 2, 2, 2, 2, 3, 3, 3, 3,
4, 4, 5, 5, 6, 6, 7, 7, 8
};
static const unsigned int above_context_index[25] =
{
0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3, 0, 1, 2, 3,
4, 5, 4, 5, 6, 7, 6, 7, 8
};
#define X(n) ((n) * PREV_COEFF_CONTEXTS * ENTROPY_NODES)
static const unsigned int bands_x[16] =
{
X(0), X(1), X(2), X(3), X(6), X(4), X(5), X(6),
X(6), X(6), X(6), X(6), X(6), X(6), X(6), X(7)
};
#undef X
static const struct extrabits extrabits[MAX_ENTROPY_TOKENS] =
{
{ 0, -1, { 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0 } }, //ZERO_TOKEN
{ 1, 0, { 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0 } }, //ONE_TOKEN
{ 2, 0, { 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0 } }, //TWO_TOKEN
{ 3, 0, { 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0 } }, //THREE_TOKEN
{ 4, 0, { 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0 } }, //FOUR_TOKEN
{ 5, 0, {159, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0 } }, //DCT_VAL_CATEGORY1
{ 7, 1, {145, 165, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0 } }, //DCT_VAL_CATEGORY2
{11, 2, {140, 148, 173, 0, 0, 0,
0, 0, 0, 0, 0, 0 } }, //DCT_VAL_CATEGORY3
Bankoski, et al. Informational [Page 233]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{19, 3, {135, 140, 155, 176, 0, 0,
0, 0, 0, 0, 0, 0 } }, //DCT_VAL_CATEGORY4
{35, 4, {130, 134, 141, 157, 180, 0,
0, 0, 0, 0, 0, 0 } }, //DCT_VAL_CATEGORY5
{67, 10, {129, 130, 133, 140, 153, 177,
196, 230, 243, 254, 254, 0 } }, //DCT_VAL_CATEGORY6
{ 0, -1, { 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0 } }, // EOB TOKEN
};
static const unsigned int zigzag[16] =
{
0, 1, 4, 8, 5, 2, 3, 6, 9, 12, 13, 10, 7, 11, 14, 15
};
#define DECODE_AND_APPLYSIGN(value_to_sign) \
v = (bool_get_bit(bool) ? -value_to_sign \
: value_to_sign) * dqf[!!c];
#define DECODE_AND_BRANCH_IF_ZERO(probability,branch) \
if (!bool_get(bool, probability)) goto branch;
#define DECODE_AND_LOOP_IF_ZERO(probability,branch) \
if (!bool_get(bool, probability)) \
{ \
prob = type_probs; \
if (c<15) {\
++c; \
prob += bands_x[c]; \
goto branch; \
}\
else \
goto BLOCK_FINISHED; /* for malformed input */\
}
#define DECODE_SIGN_WRITE_COEFF_AND_CHECK_EXIT(val) \
DECODE_AND_APPLYSIGN(val) \
prob = type_probs + (ENTROPY_NODES*2); \
if (c < 15){\
b_tokens[zigzag[c]] = v; \
++c; \
goto DO_WHILE; }\
b_tokens[zigzag[15]] = v; \
goto BLOCK_FINISHED;
Bankoski, et al. Informational [Page 234]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
#define DECODE_EXTRABIT_AND_ADJUST_VAL(t,bits_count)\
val += bool_get(bool, extrabits[t].probs[bits_count]) << \
bits_count;
static int
decode_mb_tokens(struct bool_decoder *bool,
token_entropy_ctx_t left,
token_entropy_ctx_t above,
short *tokens,
enum prediction_mode mode,
coeff_probs_table_t probs,
short factor[TOKEN_BLOCK_TYPES][2])
{
int i, stop, type;
int c, t, v;
int val, bits_count;
int eob_mask;
short *b_tokens; // tokens for this block
unsigned char *type_probs; // probabilities for this block type
unsigned char *prob;
short *dqf;
eob_mask = 0;
if (mode != B_PRED && mode != SPLITMV)
{
i = 24;
stop = 24;
type = 1;
b_tokens = tokens + 24 * 16;
dqf = factor[TOKEN_BLOCK_Y2];
}
else
{
i = 0;
stop = 16;
type = 3;
b_tokens = tokens;
dqf = factor[TOKEN_BLOCK_Y1];
}
/* Save a pointer to the coefficient probs for the current type.
* Need to repeat this whenever type changes.
*/
type_probs = probs[type][0][0];
Bankoski, et al. Informational [Page 235]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
BLOCK_LOOP:
t = left[left_context_index[i]] + above[above_context_index[i]];
c = !type; /* all blocks start at 0 except type 0, which starts
* at 1. */
prob = type_probs;
prob += t * ENTROPY_NODES;
DO_WHILE:
prob += bands_x[c];
DECODE_AND_BRANCH_IF_ZERO(prob[EOB_CONTEXT_NODE],
BLOCK_FINISHED);
CHECK_0_:
DECODE_AND_LOOP_IF_ZERO(prob[ZERO_CONTEXT_NODE], CHECK_0_);
DECODE_AND_BRANCH_IF_ZERO(prob[ONE_CONTEXT_NODE],
ONE_CONTEXT_NODE_0_);
DECODE_AND_BRANCH_IF_ZERO(prob[LOW_VAL_CONTEXT_NODE],
LOW_VAL_CONTEXT_NODE_0_);
DECODE_AND_BRANCH_IF_ZERO(prob[HIGH_LOW_CONTEXT_NODE],
HIGH_LOW_CONTEXT_NODE_0_);
DECODE_AND_BRANCH_IF_ZERO(prob[CAT_THREEFOUR_CONTEXT_NODE],
CAT_THREEFOUR_CONTEXT_NODE_0_);
DECODE_AND_BRANCH_IF_ZERO(prob[CAT_FIVE_CONTEXT_NODE],
CAT_FIVE_CONTEXT_NODE_0_);
val = extrabits[DCT_VAL_CATEGORY6].min_val;
bits_count = extrabits[DCT_VAL_CATEGORY6].length;
do
{
DECODE_EXTRABIT_AND_ADJUST_VAL(DCT_VAL_CATEGORY6,
bits_count);
bits_count --;
}
while (bits_count >= 0);
DECODE_SIGN_WRITE_COEFF_AND_CHECK_EXIT(val);
CAT_FIVE_CONTEXT_NODE_0_:
val = extrabits[DCT_VAL_CATEGORY5].min_val;
DECODE_EXTRABIT_AND_ADJUST_VAL(DCT_VAL_CATEGORY5, 4);
DECODE_EXTRABIT_AND_ADJUST_VAL(DCT_VAL_CATEGORY5, 3);
DECODE_EXTRABIT_AND_ADJUST_VAL(DCT_VAL_CATEGORY5, 2);
DECODE_EXTRABIT_AND_ADJUST_VAL(DCT_VAL_CATEGORY5, 1);
DECODE_EXTRABIT_AND_ADJUST_VAL(DCT_VAL_CATEGORY5, 0);
DECODE_SIGN_WRITE_COEFF_AND_CHECK_EXIT(val);
Bankoski, et al. Informational [Page 236]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
CAT_THREEFOUR_CONTEXT_NODE_0_:
DECODE_AND_BRANCH_IF_ZERO(prob[CAT_THREE_CONTEXT_NODE],
CAT_THREE_CONTEXT_NODE_0_);
val = extrabits[DCT_VAL_CATEGORY4].min_val;
DECODE_EXTRABIT_AND_ADJUST_VAL(DCT_VAL_CATEGORY4, 3);
DECODE_EXTRABIT_AND_ADJUST_VAL(DCT_VAL_CATEGORY4, 2);
DECODE_EXTRABIT_AND_ADJUST_VAL(DCT_VAL_CATEGORY4, 1);
DECODE_EXTRABIT_AND_ADJUST_VAL(DCT_VAL_CATEGORY4, 0);
DECODE_SIGN_WRITE_COEFF_AND_CHECK_EXIT(val);
CAT_THREE_CONTEXT_NODE_0_:
val = extrabits[DCT_VAL_CATEGORY3].min_val;
DECODE_EXTRABIT_AND_ADJUST_VAL(DCT_VAL_CATEGORY3, 2);
DECODE_EXTRABIT_AND_ADJUST_VAL(DCT_VAL_CATEGORY3, 1);
DECODE_EXTRABIT_AND_ADJUST_VAL(DCT_VAL_CATEGORY3, 0);
DECODE_SIGN_WRITE_COEFF_AND_CHECK_EXIT(val);
HIGH_LOW_CONTEXT_NODE_0_:
DECODE_AND_BRANCH_IF_ZERO(prob[CAT_ONE_CONTEXT_NODE],
CAT_ONE_CONTEXT_NODE_0_);
val = extrabits[DCT_VAL_CATEGORY2].min_val;
DECODE_EXTRABIT_AND_ADJUST_VAL(DCT_VAL_CATEGORY2, 1);
DECODE_EXTRABIT_AND_ADJUST_VAL(DCT_VAL_CATEGORY2, 0);
DECODE_SIGN_WRITE_COEFF_AND_CHECK_EXIT(val);
CAT_ONE_CONTEXT_NODE_0_:
val = extrabits[DCT_VAL_CATEGORY1].min_val;
DECODE_EXTRABIT_AND_ADJUST_VAL(DCT_VAL_CATEGORY1, 0);
DECODE_SIGN_WRITE_COEFF_AND_CHECK_EXIT(val);
LOW_VAL_CONTEXT_NODE_0_:
DECODE_AND_BRANCH_IF_ZERO(prob[TWO_CONTEXT_NODE],
TWO_CONTEXT_NODE_0_);
DECODE_AND_BRANCH_IF_ZERO(prob[THREE_CONTEXT_NODE],
THREE_CONTEXT_NODE_0_);
DECODE_SIGN_WRITE_COEFF_AND_CHECK_EXIT(4);
THREE_CONTEXT_NODE_0_:
DECODE_SIGN_WRITE_COEFF_AND_CHECK_EXIT(3);
TWO_CONTEXT_NODE_0_:
DECODE_SIGN_WRITE_COEFF_AND_CHECK_EXIT(2);
ONE_CONTEXT_NODE_0_:
DECODE_AND_APPLYSIGN(1);
prob = type_probs + ENTROPY_NODES;
Bankoski, et al. Informational [Page 237]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
if (c < 15)
{
b_tokens[zigzag[c]] = v;
++c;
goto DO_WHILE;
}
b_tokens[zigzag[15]] = v;
BLOCK_FINISHED:
eob_mask |= (c > 1) << i;
t = (c != !type); // any non-zero data?
eob_mask |= t << 31;
left[left_context_index[i]] = above[above_context_index[i]] = t;
b_tokens += 16;
i++;
if (i < stop)
goto BLOCK_LOOP;
if (i == 25)
{
type = 0;
i = 0;
stop = 16;
type_probs = probs[type][0][0];
b_tokens = tokens;
dqf = factor[TOKEN_BLOCK_Y1];
goto BLOCK_LOOP;
}
if (i == 16)
{
type = 2;
type_probs = probs[type][0][0];
stop = 24;
dqf = factor[TOKEN_BLOCK_UV];
goto BLOCK_LOOP;
}
return eob_mask;
}
Bankoski, et al. Informational [Page 238]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
static void
reset_row_context(token_entropy_ctx_t *left)
{
memset(left, 0, sizeof(*left));
}
static void
reset_above_context(token_entropy_ctx_t *above, unsigned int cols)
{
memset(above, 0, cols * sizeof(*above));
}
static void
reset_mb_context(token_entropy_ctx_t *left,
token_entropy_ctx_t *above,
enum prediction_mode mode)
{
/* Reset the macroblock context on the left and right. We have
* to preserve the context of the second order block if this mode
* would not have updated it.
*/
memset(left, 0, sizeof((*left)[0]) * 8);
memset(above, 0, sizeof((*above)[0]) * 8);
if (mode != B_PRED && mode != SPLITMV)
{
(*left)[8] = 0;
(*above)[8] = 0;
}
}
void
vp8_dixie_tokens_process_row(struct vp8_decoder_ctx *ctx,
unsigned int partition,
unsigned int row,
unsigned int start_col,
unsigned int num_cols)
{
struct token_decoder *tokens = &ctx->tokens[partition];
short coeffs = tokens->coeffs + 25 * 16 * start_col;
unsigned int col;
token_entropy_ctx_t *above = ctx->above_token_entropy_ctx
+ start_col;
token_entropy_ctx_t *left = &tokens->left_token_entropy_ctx;
struct mb_info *mbi = ctx->mb_info_rows[row] + start_col;
Bankoski, et al. Informational [Page 239]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
if (row == 0)
reset_above_context(above, num_cols);
if (start_col == 0)
reset_row_context(left);
for (col = start_col; col < start_col + num_cols; col++)
{
memset(coeffs, 0, 25 * 16 * sizeof(short));
if (mbi->base.skip_coeff)
{
reset_mb_context(left, above, mbi->base.y_mode);
mbi->base.eob_mask = 0;
}
else
{
struct dequant_factors *dqf;
dqf = ctx->dequant_factors + mbi->base.segment_id;
mbi->base.eob_mask =
decode_mb_tokens(&tokens->bool,
*left, *above,
coeffs,
mbi->base.y_mode,
ctx->entropy_hdr.coeff_probs,
dqf->factor);
}
above++;
mbi++;
coeffs += 25 * 16;
}
}
void
vp8_dixie_tokens_init(struct vp8_decoder_ctx *ctx)
{
unsigned int partitions = ctx->token_hdr.partitions;
if (ctx->frame_hdr.frame_size_updated)
{
unsigned int i;
unsigned int coeff_row_sz =
ctx->mb_cols * 25 * 16 * sizeof(short);
Bankoski, et al. Informational [Page 240]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
for (i = 0; i < partitions; i++)
{
free(ctx->tokens[i].coeffs);
ctx->tokens[i].coeffs = memalign(16, coeff_row_sz);
if (!ctx->tokens[i].coeffs)
vpx_internal_error(&ctx->error, VPX_CODEC_MEM_ERROR,
NULL);
}
free(ctx->above_token_entropy_ctx);
ctx->above_token_entropy_ctx =
calloc(ctx->mb_cols,
sizeof(*ctx->above_token_entropy_ctx));
if (!ctx->above_token_entropy_ctx)
vpx_internal_error(&ctx->error,
VPX_CODEC_MEM_ERROR, NULL);
}
}
void
vp8_dixie_tokens_destroy(struct vp8_decoder_ctx *ctx)
{
int i;
for (i = 0; i < MAX_PARTITIONS; i++)
free(ctx->tokens[i].coeffs);
free(ctx->above_token_entropy_ctx);
}
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 241]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
20.17. tokens.h
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#ifndef TOKENS_H
#define TOKENS_H
void
vp8_dixie_tokens_init(struct vp8_decoder_ctx *ctx);
void
vp8_dixie_tokens_destroy(struct vp8_decoder_ctx *ctx);
void
vp8_dixie_tokens_process_row(struct vp8_decoder_ctx *ctx,
unsigned int partition,
unsigned int row,
unsigned int start_col,
unsigned int num_cols);
#endif
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 242]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
20.18. vp8_prob_data.h
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
static const
unsigned char k_coeff_entropy_update_probs[BLOCK_TYPES][COEFF_BANDS]
[PREV_COEFF_CONTEXTS]
[ENTROPY_NODES] =
{
{
{
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
},
{
{176, 246, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{223, 241, 252, 255, 255, 255, 255, 255, 255, 255, 255},
{249, 253, 253, 255, 255, 255, 255, 255, 255, 255, 255},
},
{
{255, 244, 252, 255, 255, 255, 255, 255, 255, 255, 255},
{234, 254, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{253, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
},
{
{255, 246, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{239, 253, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{254, 255, 254, 255, 255, 255, 255, 255, 255, 255, 255},
},
{
{255, 248, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{251, 255, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
},
Bankoski, et al. Informational [Page 243]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{
{255, 253, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{251, 254, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{254, 255, 254, 255, 255, 255, 255, 255, 255, 255, 255},
},
{
{255, 254, 253, 255, 254, 255, 255, 255, 255, 255, 255},
{250, 255, 254, 255, 254, 255, 255, 255, 255, 255, 255},
{254, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
},
{
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
},
},
{
{
{217, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{225, 252, 241, 253, 255, 255, 254, 255, 255, 255, 255},
{234, 250, 241, 250, 253, 255, 253, 254, 255, 255, 255},
},
{
{255, 254, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{223, 254, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{238, 253, 254, 254, 255, 255, 255, 255, 255, 255, 255},
},
{
{255, 248, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{249, 254, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
},
{
{255, 253, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{247, 254, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
},
{
{255, 253, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{252, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
},
{
{255, 254, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{253, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
},
Bankoski, et al. Informational [Page 244]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{
{255, 254, 253, 255, 255, 255, 255, 255, 255, 255, 255},
{250, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{254, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
},
{
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
},
},
{
{
{186, 251, 250, 255, 255, 255, 255, 255, 255, 255, 255},
{234, 251, 244, 254, 255, 255, 255, 255, 255, 255, 255},
{251, 251, 243, 253, 254, 255, 254, 255, 255, 255, 255},
},
{
{255, 253, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{236, 253, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{251, 253, 253, 254, 254, 255, 255, 255, 255, 255, 255},
},
{
{255, 254, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{254, 254, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
},
{
{255, 254, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{254, 254, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{254, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
},
{
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{254, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
},
{
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
},
{
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
},
Bankoski, et al. Informational [Page 245]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
},
},
{
{
{248, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{250, 254, 252, 254, 255, 255, 255, 255, 255, 255, 255},
{248, 254, 249, 253, 255, 255, 255, 255, 255, 255, 255},
},
{
{255, 253, 253, 255, 255, 255, 255, 255, 255, 255, 255},
{246, 253, 253, 255, 255, 255, 255, 255, 255, 255, 255},
{252, 254, 251, 254, 254, 255, 255, 255, 255, 255, 255},
},
{
{255, 254, 252, 255, 255, 255, 255, 255, 255, 255, 255},
{248, 254, 253, 255, 255, 255, 255, 255, 255, 255, 255},
{253, 255, 254, 254, 255, 255, 255, 255, 255, 255, 255},
},
{
{255, 251, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{245, 251, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{253, 253, 254, 255, 255, 255, 255, 255, 255, 255, 255},
},
{
{255, 251, 253, 255, 255, 255, 255, 255, 255, 255, 255},
{252, 253, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{255, 254, 255, 255, 255, 255, 255, 255, 255, 255, 255},
},
{
{255, 252, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{249, 255, 254, 255, 255, 255, 255, 255, 255, 255, 255},
{255, 255, 254, 255, 255, 255, 255, 255, 255, 255, 255},
},
{
{255, 255, 253, 255, 255, 255, 255, 255, 255, 255, 255},
{250, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
},
Bankoski, et al. Informational [Page 246]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{254, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
{255, 255, 255, 255, 255, 255, 255, 255, 255, 255, 255},
},
},
};
static const
unsigned char k_default_y_mode_probs [] =
{ 112, 86, 140, 37};
static const
unsigned char k_default_uv_mode_probs [] =
{ 162, 101, 204};
static const
unsigned char k_default_coeff_probs [BLOCK_TYPES][COEFF_BANDS]
[PREV_COEFF_CONTEXTS][ENTROPY_NODES] =
{
{ /* block type 0 */
{ /* coeff band 0 */
{ 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128},
{ 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128},
{ 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128}
},
{ /* coeff band 1 */
{ 253, 136, 254, 255, 228, 219, 128, 128, 128, 128, 128},
{ 189, 129, 242, 255, 227, 213, 255, 219, 128, 128, 128},
{ 106, 126, 227, 252, 214, 209, 255, 255, 128, 128, 128}
},
{ /* coeff band 2 */
{ 1, 98, 248, 255, 236, 226, 255, 255, 128, 128, 128},
{ 181, 133, 238, 254, 221, 234, 255, 154, 128, 128, 128},
{ 78, 134, 202, 247, 198, 180, 255, 219, 128, 128, 128}
},
{ /* coeff band 3 */
{ 1, 185, 249, 255, 243, 255, 128, 128, 128, 128, 128},
{ 184, 150, 247, 255, 236, 224, 128, 128, 128, 128, 128},
{ 77, 110, 216, 255, 236, 230, 128, 128, 128, 128, 128}
},
Bankoski, et al. Informational [Page 247]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{ /* coeff band 4 */
{ 1, 101, 251, 255, 241, 255, 128, 128, 128, 128, 128},
{ 170, 139, 241, 252, 236, 209, 255, 255, 128, 128, 128},
{ 37, 116, 196, 243, 228, 255, 255, 255, 128, 128, 128}
},
{ /* coeff band 5 */
{ 1, 204, 254, 255, 245, 255, 128, 128, 128, 128, 128},
{ 207, 160, 250, 255, 238, 128, 128, 128, 128, 128, 128},
{ 102, 103, 231, 255, 211, 171, 128, 128, 128, 128, 128}
},
{ /* coeff band 6 */
{ 1, 152, 252, 255, 240, 255, 128, 128, 128, 128, 128},
{ 177, 135, 243, 255, 234, 225, 128, 128, 128, 128, 128},
{ 80, 129, 211, 255, 194, 224, 128, 128, 128, 128, 128}
},
{ /* coeff band 7 */
{ 1, 1, 255, 128, 128, 128, 128, 128, 128, 128, 128},
{ 246, 1, 255, 128, 128, 128, 128, 128, 128, 128, 128},
{ 255, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128}
}
},
{ /* block type 1 */
{ /* coeff band 0 */
{ 198, 35, 237, 223, 193, 187, 162, 160, 145, 155, 62},
{ 131, 45, 198, 221, 172, 176, 220, 157, 252, 221, 1},
{ 68, 47, 146, 208, 149, 167, 221, 162, 255, 223, 128}
},
{ /* coeff band 1 */
{ 1, 149, 241, 255, 221, 224, 255, 255, 128, 128, 128},
{ 184, 141, 234, 253, 222, 220, 255, 199, 128, 128, 128},
{ 81, 99, 181, 242, 176, 190, 249, 202, 255, 255, 128}
},
{ /* coeff band 2 */
{ 1, 129, 232, 253, 214, 197, 242, 196, 255, 255, 128},
{ 99, 121, 210, 250, 201, 198, 255, 202, 128, 128, 128},
{ 23, 91, 163, 242, 170, 187, 247, 210, 255, 255, 128}
},
{ /* coeff band 3 */
{ 1, 200, 246, 255, 234, 255, 128, 128, 128, 128, 128},
{ 109, 178, 241, 255, 231, 245, 255, 255, 128, 128, 128},
{ 44, 130, 201, 253, 205, 192, 255, 255, 128, 128, 128}
},
{ /* coeff band 4 */
{ 1, 132, 239, 251, 219, 209, 255, 165, 128, 128, 128},
{ 94, 136, 225, 251, 218, 190, 255, 255, 128, 128, 128},
{ 22, 100, 174, 245, 186, 161, 255, 199, 128, 128, 128}
},
Bankoski, et al. Informational [Page 248]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{ /* coeff band 5 */
{ 1, 182, 249, 255, 232, 235, 128, 128, 128, 128, 128},
{ 124, 143, 241, 255, 227, 234, 128, 128, 128, 128, 128},
{ 35, 77, 181, 251, 193, 211, 255, 205, 128, 128, 128}
},
{ /* coeff band 6 */
{ 1, 157, 247, 255, 236, 231, 255, 255, 128, 128, 128},
{ 121, 141, 235, 255, 225, 227, 255, 255, 128, 128, 128},
{ 45, 99, 188, 251, 195, 217, 255, 224, 128, 128, 128}
},
{ /* coeff band 7 */
{ 1, 1, 251, 255, 213, 255, 128, 128, 128, 128, 128},
{ 203, 1, 248, 255, 255, 128, 128, 128, 128, 128, 128},
{ 137, 1, 177, 255, 224, 255, 128, 128, 128, 128, 128}
}
},
{ /* block type 2 */
{ /* coeff band 0 */
{ 253, 9, 248, 251, 207, 208, 255, 192, 128, 128, 128},
{ 175, 13, 224, 243, 193, 185, 249, 198, 255, 255, 128},
{ 73, 17, 171, 221, 161, 179, 236, 167, 255, 234, 128}
},
{ /* coeff band 1 */
{ 1, 95, 247, 253, 212, 183, 255, 255, 128, 128, 128},
{ 239, 90, 244, 250, 211, 209, 255, 255, 128, 128, 128},
{ 155, 77, 195, 248, 188, 195, 255, 255, 128, 128, 128}
},
{ /* coeff band 2 */
{ 1, 24, 239, 251, 218, 219, 255, 205, 128, 128, 128},
{ 201, 51, 219, 255, 196, 186, 128, 128, 128, 128, 128},
{ 69, 46, 190, 239, 201, 218, 255, 228, 128, 128, 128}
},
{ /* coeff band 3 */
{ 1, 191, 251, 255, 255, 128, 128, 128, 128, 128, 128},
{ 223, 165, 249, 255, 213, 255, 128, 128, 128, 128, 128},
{ 141, 124, 248, 255, 255, 128, 128, 128, 128, 128, 128}
},
{ /* coeff band 4 */
{ 1, 16, 248, 255, 255, 128, 128, 128, 128, 128, 128},
{ 190, 36, 230, 255, 236, 255, 128, 128, 128, 128, 128},
{ 149, 1, 255, 128, 128, 128, 128, 128, 128, 128, 128}
},
{ /* coeff band 5 */
{ 1, 226, 255, 128, 128, 128, 128, 128, 128, 128, 128},
{ 247, 192, 255, 128, 128, 128, 128, 128, 128, 128, 128},
{ 240, 128, 255, 128, 128, 128, 128, 128, 128, 128, 128}
},
Bankoski, et al. Informational [Page 249]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{ /* coeff band 6 */
{ 1, 134, 252, 255, 255, 128, 128, 128, 128, 128, 128},
{ 213, 62, 250, 255, 255, 128, 128, 128, 128, 128, 128},
{ 55, 93, 255, 128, 128, 128, 128, 128, 128, 128, 128}
},
{ /* coeff band 7 */
{ 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128},
{ 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128},
{ 128, 128, 128, 128, 128, 128, 128, 128, 128, 128, 128}
}
},
{ /* block type 3 */
{ /* coeff band 0 */
{ 202, 24, 213, 235, 186, 191, 220, 160, 240, 175, 255},
{ 126, 38, 182, 232, 169, 184, 228, 174, 255, 187, 128},
{ 61, 46, 138, 219, 151, 178, 240, 170, 255, 216, 128}
},
{ /* coeff band 1 */
{ 1, 112, 230, 250, 199, 191, 247, 159, 255, 255, 128},
{ 166, 109, 228, 252, 211, 215, 255, 174, 128, 128, 128},
{ 39, 77, 162, 232, 172, 180, 245, 178, 255, 255, 128}
},
{ /* coeff band 2 */
{ 1, 52, 220, 246, 198, 199, 249, 220, 255, 255, 128},
{ 124, 74, 191, 243, 183, 193, 250, 221, 255, 255, 128},
{ 24, 71, 130, 219, 154, 170, 243, 182, 255, 255, 128}
},
{ /* coeff band 3 */
{ 1, 182, 225, 249, 219, 240, 255, 224, 128, 128, 128},
{ 149, 150, 226, 252, 216, 205, 255, 171, 128, 128, 128},
{ 28, 108, 170, 242, 183, 194, 254, 223, 255, 255, 128}
},
{ /* coeff band 4 */
{ 1, 81, 230, 252, 204, 203, 255, 192, 128, 128, 128},
{ 123, 102, 209, 247, 188, 196, 255, 233, 128, 128, 128},
{ 20, 95, 153, 243, 164, 173, 255, 203, 128, 128, 128}
},
{ /* coeff band 5 */
{ 1, 222, 248, 255, 216, 213, 128, 128, 128, 128, 128},
{ 168, 175, 246, 252, 235, 205, 255, 255, 128, 128, 128},
{ 47, 116, 215, 255, 211, 212, 255, 255, 128, 128, 128}
},
{ /* coeff band 6 */
{ 1, 121, 236, 253, 212, 214, 255, 255, 128, 128, 128},
{ 141, 84, 213, 252, 201, 202, 255, 219, 128, 128, 128},
{ 42, 80, 160, 240, 162, 185, 255, 205, 128, 128, 128}
},
Bankoski, et al. Informational [Page 250]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
{ /* coeff band 7 */
{ 1, 1, 255, 128, 128, 128, 128, 128, 128, 128, 128},
{ 244, 1, 255, 128, 128, 128, 128, 128, 128, 128, 128},
{ 238, 1, 255, 128, 128, 128, 128, 128, 128, 128, 128}
}
}
};
static const
unsigned char k_mv_entropy_update_probs[2][MV_PROB_CNT] =
{
{
237,
246,
253, 253, 254, 254, 254, 254, 254,
254, 254, 254, 254, 254, 250, 250, 252, 254, 254
},
{
231,
243,
245, 253, 254, 254, 254, 254, 254,
254, 254, 254, 254, 254, 251, 251, 254, 254, 254
}
};
static const
unsigned char k_default_mv_probs[2][MV_PROB_CNT] =
{
{ // row
162, // is short
128, // sign
225, 146, 172, 147, 214, 39, 156, // short tree
128, 129, 132, 75, 145, 178, 206, 239, 254, 254 // long bits
},
{
164,
128,
204, 170, 119, 235, 140, 230, 228,
128, 130, 130, 74, 148, 180, 203, 236, 254, 254
}
};
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 251]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
20.19. vpx_codec_internal.h
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
/*!\file vpx_codec_internal.h
* \brief Describes the decoder algorithm interface for algorithm
* implementations.
*
* This file defines the private structures and data types that are
* only relevant to implementing an algorithm, as opposed to using
* it.
*
* To create a decoder algorithm class, an interface structure is put
* into the global namespace:
* <pre>
* my_codec.c:
* vpx_codec_iface_t my_codec = {
* "My Codec v1.0",
* VPX_CODEC_ALG_ABI_VERSION,
* ...
* };
* </pre>
*
* An application instantiates a specific decoder instance by using
* vpx_codec_init() and a pointer to the algorithm's interface
* structure:
* <pre>
* my_app.c:
* extern vpx_codec_iface_t my_codec;
* {
* vpx_codec_ctx_t algo;
* res = vpx_codec_init(&algo, &my_codec);
* }
* </pre>
*
Bankoski, et al. Informational [Page 252]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
* Once initialized, the instance is managed using other functions
* from the vpx_codec_* family.
*/
#ifndef VPX_CODEC_INTERNAL_H
#define VPX_CODEC_INTERNAL_H
#include "vpx_decoder.h"
#include <stdarg.h>
/*!\brief Current ABI version number
*
* \internal
* If this file is altered in any way that changes the Application
* Binary Interface (ABI), this value must be bumped. Examples
* include, but are not limited to, changing types, removing or
* reassigning enums, adding/removing/rearranging fields to
* structures.
*/
#define VPX_CODEC_INTERNAL_ABI_VERSION (3)
typedef struct vpx_codec_alg_priv vpx_codec_alg_priv_t;
/*!\brief init function pointer prototype
*
* Performs algorithm-specific initialization of the decoder context.
* This function is called by the generic vpx_codec_init() wrapper
* function, so plugins implementing this interface may trust the
* input parameters to be properly initialized.
*
* \param[in] ctx Pointer to this instance's context
* \retval #VPX_CODEC_OK
* The input stream was recognized and decoder initialized.
* \retval #VPX_CODEC_MEM_ERROR
* Memory operation failed.
*/
typedef vpx_codec_err_t (*vpx_codec_init_fn_t)(vpx_codec_ctx_t *ctx);
Bankoski, et al. Informational [Page 253]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/*!\brief destroy function pointer prototype
*
* Performs algorithm-specific destruction of the decoder context.
* This function is called by the generic vpx_codec_destroy() wrapper
* function, so plugins implementing this interface may trust the
* input parameters to be properly initialized.
*
* \param[in] ctx Pointer to this instance's context
* \retval #VPX_CODEC_OK
* The input stream was recognized and decoder initialized.
* \retval #VPX_CODEC_MEM_ERROR
* Memory operation failed.
*/
typedef vpx_codec_err_t (*vpx_codec_destroy_fn_t)(
vpx_codec_alg_priv_t *ctx);
/*!\brief parse stream info function pointer prototype
*
* Performs high level parsing of the bitstream. This function is
* called by the generic vpx_codec_parse_stream() wrapper function,
* so plugins implementing this interface may trust the input
* parameters to be properly initialized.
*
* \param[in] data Pointer to a block of data to parse
* \param[in] data_sz Size of the data buffer
* \param[in,out] si Pointer to stream info to update. The
* size member \ref MUST be properly
* initialized, but \ref MAY be clobbered by
* the algorithm. This parameter \ref MAY
* be NULL.
*
* \retval #VPX_CODEC_OK
* Bitstream is parsable and stream information updated
*/
typedef vpx_codec_err_t (*vpx_codec_peek_si_fn_t)(
const uint8_t *data,
unsigned int data_sz,
vpx_codec_stream_info_t *si);
Bankoski, et al. Informational [Page 254]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/*!\brief Return information about the current stream.
*
* Returns information about the stream that has been parsed during
* decoding.
*
* \param[in] ctx Pointer to this instance's context
* \param[in,out] si Pointer to stream info to update. The
* size member \ref MUST be properly
* initialized, but \ref MAY be clobbered by
* the algorithm. This parameter \ref MAY
* be NULL.
*
* \retval #VPX_CODEC_OK
* Bitstream is parsable and stream information updated
*/
typedef vpx_codec_err_t (*vpx_codec_get_si_fn_t)(
vpx_codec_alg_priv_t *ctx,
vpx_codec_stream_info_t *si);
/*!\brief control function pointer prototype
*
* This function is used to exchange algorithm-specific data with the
* decoder instance. This can be used to implement features specific
* to a particular algorithm.
*
* This function is called by the generic vpx_codec_control() wrapper
* function, so plugins implementing this interface may trust the
* input parameters to be properly initialized. However, this
* interface does not provide type safety for the exchanged data or
* assign meanings to the control codes. Those details should be
* specified in the algorithm's header file. In particular, the
* ctrl_id parameter is guaranteed to exist in the algorithm's
* control mapping table, and the data parameter may be NULL.
*
*
* \param[in] ctx Pointer to this instance's context
* \param[in] ctrl_id Algorithm-specific control identifier
* \param[in,out] data Data to exchange with algorithm instance.
*
* \retval #VPX_CODEC_OK
* The internal state data was deserialized.
*/
typedef vpx_codec_err_t (*vpx_codec_control_fn_t)(
vpx_codec_alg_priv_t *ctx,
int ctrl_id,
va_list ap);
Bankoski, et al. Informational [Page 255]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/*!\brief control function pointer mapping
*
* This structure stores the mapping between control identifiers and
* implementing functions. Each algorithm provides a list of these
* mappings. This list is searched by the vpx_codec_control()
* wrapper function to determine which function to invoke. The
* special value {0, NULL} is used to indicate end-of-list, and must
* be present. The special value {0, <non-null>} can be used as a
* catch-all mapping. This implies that ctrl_id values chosen by the
* algorithm \ref MUST be non-zero.
*/
typedef const struct
{
int ctrl_id;
vpx_codec_control_fn_t fn;
} vpx_codec_ctrl_fn_map_t;
/*!\brief decode data function pointer prototype
*
* Processes a buffer of coded data. If the processing results in a
* new decoded frame becoming available, #VPX_CODEC_CB_PUT_SLICE and
* #VPX_CODEC_CB_PUT_FRAME events are generated as appropriate.
* This function is called by the generic vpx_codec_decode() wrapper
* function, so plugins implementing this interface may trust the
* input parameters to be properly initialized.
*
* \param[in] ctx Pointer to this instance's context
* \param[in] data Pointer to this block of new coded data.
* If NULL, a #VPX_CODEC_CB_PUT_FRAME event is
* posted for the previously decoded frame.
* \param[in] data_sz Size of the coded data, in bytes.
*
* \return Returns #VPX_CODEC_OK if the coded data was processed
* completely and future pictures can be decoded without
* error. Otherwise, see the descriptions of the other error
* codes in ::vpx_codec_err_t for recoverability
* capabilities.
*/
typedef vpx_codec_err_t (*vpx_codec_decode_fn_t)(
vpx_codec_alg_priv_t *ctx,
const uint8_t *data,
unsigned int data_sz,
void *user_priv,
long deadline);
Bankoski, et al. Informational [Page 256]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/*!\brief Decoded frames iterator
*
* Iterates over a list of the frames available for display. The
* iterator storage should be initialized to NULL to start the
* iteration. Iteration is complete when this function returns NULL.
*
* The list of available frames becomes valid upon completion of the
* vpx_codec_decode call, and remains valid until the next call to
* vpx_codec_decode.
*
* \param[in] ctx Pointer to this instance's context
* \param[in out] iter Iterator storage, initialized to NULL
*
* \return Returns a pointer to an image, if one is ready for
* display. Frames produced will always be in PTS
* (presentation time stamp) order.
*/
typedef vpx_image_t*(*vpx_codec_get_frame_fn_t)(
vpx_codec_alg_priv_t *ctx,
vpx_codec_iter_t *iter);
/*\brief External Memory Allocation memory map get iterator
*
* Iterates over a list of the memory maps requested by the decoder.
* The iterator storage should be initialized to NULL to start the
* iteration. Iteration is complete when this function returns NULL.
*
* \param[in out] iter Iterator storage, initialized to NULL
*
* \return Returns a pointer to a memory segment descriptor, or NULL
* to indicate end-of-list.
*/
typedef vpx_codec_err_t (*vpx_codec_get_mmap_fn_t)(
const vpx_codec_ctx_t *ctx,
vpx_codec_mmap_t *mmap,
vpx_codec_iter_t *iter);
Bankoski, et al. Informational [Page 257]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/*\brief External Memory Allocation memory map set iterator
*
* Sets a memory descriptor inside the decoder instance.
*
* \param[in] ctx Pointer to this instance's context
* \param[in] mmap Memory map to store.
*
* \retval #VPX_CODEC_OK
* The memory map was accepted and stored.
* \retval #VPX_CODEC_MEM_ERROR
* The memory map was rejected.
*/
typedef vpx_codec_err_t (*vpx_codec_set_mmap_fn_t)(
vpx_codec_ctx_t *ctx,
const vpx_codec_mmap_t *mmap);
typedef vpx_codec_err_t (*vpx_codec_encode_fn_t)(
vpx_codec_alg_priv_t *ctx,
const vpx_image_t *img,
vpx_codec_pts_t pts,
unsigned long duration,
vpx_enc_frame_flags_t flags,
unsigned long deadline);
typedef const vpx_codec_cx_pkt_t*(*vpx_codec_get_cx_data_fn_t)(
vpx_codec_alg_priv_t *ctx,
vpx_codec_iter_t *iter);
typedef vpx_codec_err_t
(*vpx_codec_enc_config_set_fn_t)(
vpx_codec_alg_priv_t *ctx,
const vpx_codec_enc_cfg_t *cfg);
typedef vpx_fixed_buf_t *
(*vpx_codec_get_global_headers_fn_t)(vpx_codec_alg_priv_t *ctx);
typedef vpx_image_t *
(*vpx_codec_get_preview_frame_fn_t)(vpx_codec_alg_priv_t *ctx);
/*!\brief usage configuration mapping
*
* This structure stores the mapping between usage identifiers and
* configuration structures. Each algorithm provides a list of these
* mappings. This list is searched by the
* vpx_codec_enc_config_default() wrapper function to determine which
Bankoski, et al. Informational [Page 258]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
* config to return. The special value {-1, {0}} is used to indicate
* end-of-list, and must be present. At least one mapping must be
* present, in addition to the end-of-list.
*
*/
typedef const struct
{
int usage;
vpx_codec_enc_cfg_t cfg;
} vpx_codec_enc_cfg_map_t;
#define NOT_IMPLEMENTED 0
/*!\brief Decoder algorithm interface
*
* All decoders \ref MUST expose a variable of this type.
*/
struct vpx_codec_iface
{
const char *name;
int abi_version;
vpx_codec_caps_t caps;
vpx_codec_init_fn_t init;
vpx_codec_destroy_fn_t destroy;
vpx_codec_ctrl_fn_map_t *ctrl_maps;
vpx_codec_get_mmap_fn_t get_mmap;
vpx_codec_set_mmap_fn_t set_mmap;
struct
{
vpx_codec_peek_si_fn_t peek_si;
vpx_codec_get_si_fn_t get_si;
vpx_codec_decode_fn_t decode;
vpx_codec_get_frame_fn_t get_frame;
} dec;
struct
{
vpx_codec_enc_cfg_map_t *cfg_maps;
vpx_codec_encode_fn_t encode;
vpx_codec_get_cx_data_fn_t get_cx_data;
vpx_codec_enc_config_set_fn_t cfg_set;
vpx_codec_get_global_headers_fn_t get_glob_hdrs;
vpx_codec_get_preview_frame_fn_t get_preview;
} enc;
};
Bankoski, et al. Informational [Page 259]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/*!\brief Callback function pointer / user data pair storage */
typedef struct vpx_codec_priv_cb_pair
{
union
{
vpx_codec_put_frame_cb_fn_t put_frame;
vpx_codec_put_slice_cb_fn_t put_slice;
};
void *user_priv;
} vpx_codec_priv_cb_pair_t;
/*!\brief Instance private storage
*
* This structure is allocated by the algorithm's init function. It
* can be extended in one of two ways. First, a second, algorithm
* specific structure can be allocated and the priv member pointed to
* it. Alternatively, this structure can be made the first member of
* the algorithm-specific structure, and the pointer casted to the
* proper type.
*/
struct vpx_codec_priv
{
unsigned int sz;
vpx_codec_iface_t *iface;
struct vpx_codec_alg_priv *alg_priv;
const char *err_detail;
vpx_codec_flags_t init_flags;
struct
{
vpx_codec_priv_cb_pair_t put_frame_cb;
vpx_codec_priv_cb_pair_t put_slice_cb;
} dec;
struct
{
struct vpx_fixed_buf cx_data_dst_buf;
unsigned int cx_data_pad_before;
unsigned int cx_data_pad_after;
vpx_codec_cx_pkt_t cx_data_pkt;
} enc;
};
#undef VPX_CTRL_USE_TYPE
#define VPX_CTRL_USE_TYPE(id, typ) \
static typ id##__value(va_list args) \
{return va_arg(args, typ);} \
static typ id##__convert(void *x)\
{\
Bankoski, et al. Informational [Page 260]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
union\
{\
void *x;\
typ d;\
} u;\
u.x = x;\
return u.d;\
}
#undef VPX_CTRL_USE_TYPE_DEPRECATED
#define VPX_CTRL_USE_TYPE_DEPRECATED(id, typ) \
static typ id##__value(va_list args) \
{return va_arg(args, typ);} \
static typ id##__convert(void *x)\
{\
union\
{\
void *x;\
typ d;\
} u;\
u.x = x;\
return u.d;\
}
#define CAST(id, arg) id##__value(arg)
#define RECAST(id, x) id##__convert(x)
/* Internal Utility Functions
*
* The following functions are intended to be used inside algorithms
* as utilities for manipulating vpx_codec_* data structures.
*/
struct vpx_codec_pkt_list
{
unsigned int cnt;
unsigned int max;
struct vpx_codec_cx_pkt pkts[1];
};
#define vpx_codec_pkt_list_decl(n)\
union {struct vpx_codec_pkt_list head;\
struct {struct vpx_codec_pkt_list head;\
struct vpx_codec_cx_pkt pkts[n];} alloc;}
Bankoski, et al. Informational [Page 261]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
#define vpx_codec_pkt_list_init(m)\
(m)->alloc.head.cnt = 0,\
(m)->alloc.head.max = \
sizeof((m)->alloc.pkts) / sizeof((m)->alloc.pkts[0])
int
vpx_codec_pkt_list_add(struct vpx_codec_pkt_list *,
const struct vpx_codec_cx_pkt *);
const vpx_codec_cx_pkt_t*
vpx_codec_pkt_list_get(struct vpx_codec_pkt_list *list,
vpx_codec_iter_t *iter);
#include <stdio.h>
#include <setjmp.h>
struct vpx_internal_error_info
{
vpx_codec_err_t error_code;
int has_detail;
char detail[80];
int setjmp;
jmp_buf jmp;
};
static void vpx_internal_error(struct vpx_internal_error_info *info,
vpx_codec_err_t error,
const char *fmt,
...)
{
va_list ap;
info->error_code = error;
info->has_detail = 0;
if (fmt)
{
size_t sz = sizeof(info->detail);
info->has_detail = 1;
va_start(ap, fmt);
vsnprintf(info->detail, sz - 1, fmt, ap);
va_end(ap);
info->detail[sz-1] = '\0';
}
Bankoski, et al. Informational [Page 262]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
if (info->setjmp)
longjmp(info->jmp, info->error_code);
}
#endif
---- End code block ----------------------------------------
20.20. vpx_decoder.h
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
/*!\defgroup decoder Decoder Algorithm Interface
* \ingroup codec
* This abstraction allows applications using this decoder to easily
* support multiple video formats with minimal code duplication.
* This section describes the interface common to all decoders.
* @{
*/
/*!\file vpx_decoder.h
* \brief Describes the decoder algorithm interface to applications.
*
* This file describes the interface between an application and a
* video decoder algorithm.
*
*/
#ifdef __cplusplus
extern "C" {
#endif
#ifndef VPX_DECODER_H
#define VPX_DECODER_H
#include "vpx_codec.h"
Bankoski, et al. Informational [Page 263]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/*!\brief Current ABI version number
*
* \internal
* If this file is altered in any way that changes the ABI, this
* value must be bumped. Examples include, but are not limited
* to, changing types, removing or reassigning enums,
* adding/removing/rearranging fields to structures
*/
#define VPX_DECODER_ABI_VERSION (2 + VPX_CODEC_ABI_VERSION)
/*! \brief Decoder capabilities bitfield
*
* Each decoder advertises the capabilities it supports as part
* of its ::vpx_codec_iface_t interface structure. Capabilities
* are extra interfaces or functionality, and are not required
* to be supported by a decoder.
*
* The available flags are specified by VPX_CODEC_CAP_* defines.
*/
#define VPX_CODEC_CAP_PUT_SLICE 0x10000 /**< Will issue put_slice
callbacks */
#define VPX_CODEC_CAP_PUT_FRAME 0x20000 /**< Will issue put_frame
callbacks */
#define VPX_CODEC_CAP_POSTPROC 0x40000 /**< Can postprocess decoded
frame */
/*! \brief Initialization-time Feature Enabling
*
* Certain codec features must be known at initialization time,
* to allow for proper memory allocation.
*
* The available flags are specified by VPX_CODEC_USE_* defines.
*/
#define VPX_CODEC_USE_POSTPROC 0x10000 /**< Postprocess decoded
frame */
/*!\brief Stream properties
*
* This structure is used to query or set properties of the
* decoded stream. Algorithms may extend this structure with
* data specific to their bitstream by setting the sz member
* appropriately.
*/
Bankoski, et al. Informational [Page 264]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
typedef struct vpx_codec_stream_info
{
unsigned int sz; /**< Size of this structure */
unsigned int w; /**< Width (or 0 for unknown/default) */
unsigned int h; /**< Height (or 0 for unknown/default) */
unsigned int is_kf; /**< Current frame is a keyframe */
} vpx_codec_stream_info_t;
/* REQUIRED FUNCTIONS
*
* The following functions are required to be implemented for all
* decoders. They represent the base case functionality expected
* of all decoders.
*/
/*!\brief Initialization Configurations
*
* This structure is used to pass init time configuration options
* to the decoder.
*/
typedef struct vpx_codec_dec_cfg
{
unsigned int threads; /**< Maximum number of threads to use,
default 1 */
unsigned int w; /**< Width */
unsigned int h; /**< Height */
} vpx_codec_dec_cfg_t; /**< alias for struct vpx_codec_dec_cfg */
/*!\brief Initialize a decoder instance
*
* Initializes a decoder context using the given interface.
* Applications should call the vpx_codec_dec_init convenience
* macro instead of this function directly, to ensure that the
* ABI version number parameter is properly initialized.
*
* In XMA mode (activated by setting VPX_CODEC_USE_XMA in the
* flags parameter), the storage pointed to by the cfg parameter
* must be kept readable and stable until all memory maps have
* been set.
*
* \param[in] ctx Pointer to this instance's context.
* \param[in] iface Pointer to the algorithm interface to
* use.
* \param[in] cfg Configuration to use, if known. May be
* NULL.
Bankoski, et al. Informational [Page 265]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
* \param[in] flags Bitfield of VPX_CODEC_USE_* flags
* \param[in] ver ABI version number. Must be set to
* VPX_DECODER_ABI_VERSION
* \retval #VPX_CODEC_OK
* The decoder algorithm initialized.
* \retval #VPX_CODEC_MEM_ERROR
* Memory allocation failed.
*/
vpx_codec_err_t vpx_codec_dec_init_ver(
vpx_codec_ctx_t *ctx,
vpx_codec_iface_t *iface,
vpx_codec_dec_cfg_t *cfg,
vpx_codec_flags_t flags,
int ver);
/*!\brief Convenience macro for vpx_codec_dec_init_ver()
*
* Ensures the ABI version parameter is properly set.
*/
#define vpx_codec_dec_init(ctx, iface, cfg, flags) \
vpx_codec_dec_init_ver(ctx, iface, cfg, flags, \
VPX_DECODER_ABI_VERSION)
/*!\brief Parse stream info from a buffer
*
* Performs high level parsing of the bitstream. Construction of
* a decoder context is not necessary. Can be used to determine
* if the bitstream is of the proper format, and to extract
* information from the stream.
*
* \param[in] iface Pointer to the algorithm interface
* \param[in] data Pointer to a block of data to parse
* \param[in] data_sz Size of the data buffer
* \param[in,out] si Pointer to stream info to update. The
* size member
* \ref MUST be properly initialized, but
* \ref MAY be clobbered by the
* algorithm. This parameter \ref MAY be
* NULL.
*
* \retval #VPX_CODEC_OK
* Bitstream is parsable and stream information updated
*/
Bankoski, et al. Informational [Page 266]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
vpx_codec_err_t vpx_codec_peek_stream_info(
vpx_codec_iface_t *iface,
const uint8_t *data,
unsigned int data_sz,
vpx_codec_stream_info_t *si);
/*!\brief Return information about the current stream.
*
* Returns information about the stream that has been parsed
* during decoding.
*
* \param[in] ctx Pointer to this instance's context
* \param[in,out] si Pointer to stream info to update. The
* size member \ref MUST be properly
* initialized, but \ref MAY be clobbered
* by the algorithm. This parameter \ref
* MAY be NULL.
*
* \retval #VPX_CODEC_OK
* Bitstream is parsable and stream information updated
*/
vpx_codec_err_t vpx_codec_get_stream_info(
vpx_codec_ctx_t *ctx,
vpx_codec_stream_info_t *si);
/*!\brief Decode data
*
* Processes a buffer of coded data. If the processing results
* in a new decoded frame becoming available, PUT_SLICE and
* PUT_FRAME events may be generated, as appropriate. Encoded
* data \ref MUST be passed in DTS (decode time stamp) order.
* Frames produced will always be in PTS (presentation time
* stamp) order.
*
* \param[in] ctx Pointer to this instance's context
* \param[in] data Pointer to this block of new coded
* data. If NULL, a
* VPX_CODEC_CB_PUT_FRAME event is posted
* for the previously decoded frame.
* \param[in] data_sz Size of the coded data, in bytes.
* \param[in] user_priv Application-specific data to associate
* with this frame.
* \param[in] deadline Soft deadline the decoder should
* attempt to meet, in us. Set to zero
* for unlimited.
*
Bankoski, et al. Informational [Page 267]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
* \return Returns #VPX_CODEC_OK if the coded data was processed
* completely and future pictures can be decoded without
* error. Otherwise, see the descriptions of the other
* error codes in ::vpx_codec_err_t for recoverability
* capabilities.
*/
vpx_codec_err_t vpx_codec_decode(vpx_codec_ctx_t *ctx,
const uint8_t *data,
unsigned int data_sz,
void *user_priv,
long deadline);
/*!\brief Decoded frames iterator
*
* Iterates over a list of the frames available for display. The
* iterator storage should be initialized to NULL to start the
* iteration. Iteration is complete when this function returns
* NULL.
*
* The list of available frames becomes valid upon completion of
* the vpx_codec_decode call, and remains valid until the next
* call to vpx_codec_decode.
*
* \param[in] ctx Pointer to this instance's context
* \param[in,out] iter Iterator storage, initialized to NULL
*
* \return Returns a pointer to an image, if one is ready for
* display. Frames produced will always be in PTS
* (presentation time stamp) order.
*/
vpx_image_t *vpx_codec_get_frame(vpx_codec_ctx_t *ctx,
vpx_codec_iter_t *iter);
/*!\defgroup cap_put_frame Frame-Based Decoding Functions
*
* The following functions are required to be implemented for all
* decoders that advertise the VPX_CODEC_CAP_PUT_FRAME
* capability. Calling these functions for codecs that don't
* advertise this capability will result in an error code being
* returned, usually VPX_CODEC_ERROR
* @{
*/
Bankoski, et al. Informational [Page 268]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/*!\brief put frame callback prototype
*
* This callback is invoked by the decoder to notify the
* application of the availability of decoded image data.
*/
typedef void (*vpx_codec_put_frame_cb_fn_t)(
void *user_priv,
const vpx_image_t *img);
/*!\brief Register for notification of frame completion.
*
* Registers a given function to be called when a decoded frame
* is available.
*
* \param[in] ctx Pointer to this instance's context
* \param[in] cb Pointer to the callback function
* \param[in] user_priv User's private data
*
* \retval #VPX_CODEC_OK
* Callback successfully registered.
* \retval #VPX_CODEC_ERROR
* Decoder context not initialized, or algorithm not capable
* of posting slice completion.
*/
vpx_codec_err_t vpx_codec_register_put_frame_cb(
vpx_codec_ctx_t *ctx,
vpx_codec_put_frame_cb_fn_t cb,
void *user_priv);
/*!@} - end defgroup cap_put_frame */
/*!\defgroup cap_put_slice Slice-Based Decoding Functions
*
* The following functions are required to be implemented for all
* decoders that advertise the VPX_CODEC_CAP_PUT_SLICE
* capability. Calling these functions for codecs that don't
* advertise this capability will result in an error code being
* returned, usually VPX_CODEC_ERROR
* @{
*/
/*!\brief put slice callback prototype
*
* This callback is invoked by the decoder to notify the
* application of the availability of partially decoded image
* data.
*/
Bankoski, et al. Informational [Page 269]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
typedef void (*vpx_codec_put_slice_cb_fn_t)(
void *user_priv,
const vpx_image_t *img,
const vpx_image_rect_t *valid,
const vpx_image_rect_t *update);
/*!\brief Register for notification of slice completion.
*
* Registers a given function to be called when a decoded slice
* is available.
*
* \param[in] ctx Pointer to this instance's context
* \param[in] cb Pointer to the callback function
* \param[in] user_priv User's private data
*
* \retval #VPX_CODEC_OK
* Callback successfully registered.
* \retval #VPX_CODEC_ERROR
* Decoder context not initialized, or algorithm not capable
* of posting slice completion.
*/
vpx_codec_err_t vpx_codec_register_put_slice_cb(
vpx_codec_ctx_t *ctx,
vpx_codec_put_slice_cb_fn_t cb,
void *user_priv);
/*!@} - end defgroup cap_put_slice*/
/*!@} - end defgroup decoder*/
#endif
#ifdef __cplusplus
}
#endif
#if !defined(VPX_CODEC_DISABLE_COMPAT) || !VPX_CODEC_DISABLE_COMPAT
#include "vpx_decoder_compat.h"
#endif
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 270]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
20.21. vpx_decoder_compat.h
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
/*!\defgroup decoder Common Decoder Algorithm Interface
* This abstraction allows applications using this decoder to easily
* support multiple video formats with minimal code duplication.
* This section describes the interface common to all codecs.
* @{
*/
/*!\file
* \brief Provides a compatibility layer between version 1 and 2 of
* this API.
*
* This interface has been deprecated. Only existing code should
* make use of this interface, and therefore, it is only thinly
* documented. Existing code should be ported to the vpx_codec_*
* API.
*/
#ifdef __cplusplus
extern "C" {
#endif
#ifndef VPX_DECODER_COMPAT_H
#define VPX_DECODER_COMPAT_H
Bankoski, et al. Informational [Page 271]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/*!\brief Decoder algorithm return codes */
typedef enum {
/*!\brief Operation completed without error */
VPX_DEC_OK = VPX_CODEC_OK,
/*!\brief Unspecified error */
VPX_DEC_ERROR = VPX_CODEC_ERROR,
/*!\brief Memory operation failed */
VPX_DEC_MEM_ERROR = VPX_CODEC_MEM_ERROR,
/*!\brief ABI version mismatch */
VPX_DEC_ABI_MISMATCH = VPX_CODEC_ABI_MISMATCH,
/*!\brief The given bitstream is not supported.
*
* The bitstream was unable to be parsed at the highest
* level. The decoder is unable to proceed. This error \ref
* SHOULD be treated as fatal to the stream.
*/
VPX_DEC_UNSUP_BITSTREAM = VPX_CODEC_UNSUP_BITSTREAM,
/*!\brief Encoded bitstream uses an unsupported feature
*
* The decoder does not implement a feature required by the
* encoder. This return code should only be used for
* features that prevent future pictures from being properly
* decoded. This error \ref MAY be treated as fatal to the
* stream or \ref MAY be treated as fatal to the current
* Group of Pictures (GOP).
*/
VPX_DEC_UNSUP_FEATURE = VPX_CODEC_UNSUP_FEATURE,
/*!\brief The coded data for this stream is corrupt or
* incomplete
*
* There was a problem decoding the current frame. This
* return code should only be used for failures that prevent
* future pictures from being properly decoded. This error
* \ref MAY be treated as fatal to the stream or \ref MAY be
* treated as fatal to the current GOP. If decoding is
* continued for the current GOP, artifacts may be present.
*/
VPX_DEC_CORRUPT_FRAME = VPX_CODEC_CORRUPT_FRAME,
Bankoski, et al. Informational [Page 272]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/*!\brief An application-supplied parameter is not valid.
*
*/
VPX_DEC_INVALID_PARAM = VPX_CODEC_INVALID_PARAM,
/*!\brief An iterator reached the end of list.
*
*/
VPX_DEC_LIST_END = VPX_CODEC_LIST_END
}
vpx_dec_err_t;
/*! \brief Decoder capabilities bitfield
*
* Each decoder advertises the capabilities it supports as part
* of its ::vpx_dec_iface_t interface structure. Capabilities
* are extra interfaces or functionality, and are not required
* to be supported by a decoder.
*
* The available flags are specified by VPX_DEC_CAP_* defines.
*/
typedef int vpx_dec_caps_t;
#define VPX_DEC_CAP_PUT_SLICE 0x0001 /**< Will issue put_slice
callbacks */
#define VPX_DEC_CAP_PUT_FRAME 0x0002 /**< Will issue put_frame
callbacks */
#define VPX_DEC_CAP_XMA 0x0004 /**< Supports External Memory
Allocation */
/*!\brief Stream properties
*
* This structure is used to query or set properties of the
* decoded stream. Algorithms may extend this structure with
* data specific to their bitstream by setting the sz member
* appropriately.
*/
#if 1
typedef vpx_codec_stream_info_t vpx_dec_stream_info_t;
#else
typedef struct
{
unsigned int sz; /**< Size of this structure */
unsigned int w; /**< Width (or 0 for unknown/default) */
unsigned int h; /**< Height (or 0 for unknown/default) */
unsigned int is_kf; /**< Current frame is a keyframe */
} vpx_dec_stream_info_t;
Bankoski, et al. Informational [Page 273]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
#endif
/*!\brief Decoder interface structure.
*
* Contains function pointers and other data private to the
* decoder implementation. This structure is opaque to the
* application.
*/
typedef const struct vpx_codec_iface vpx_dec_iface_t;
typedef struct vpx_codec_priv vpx_dec_priv_t;
/*!\brief Iterator
*
* Opaque storage used for iterating over lists.
*/
typedef vpx_codec_iter_t vpx_dec_iter_t;
/*!\brief Decoder context structure
*
* All decoders \ref MUST support this context structure fully.
* In general, this data should be considered private to the
* decoder algorithm, and not be manipulated or examined by the
* calling application. Applications may reference the 'name'
* member to get a printable description of the algorithm.
*/
#if 1
typedef vpx_codec_ctx_t vpx_dec_ctx_t;
#else
typedef struct
{
const char *name; /**< Printable interface name */
vpx_dec_iface_t *iface; /**< Interface pointers */
vpx_dec_err_t err; /**< Last returned error */
vpx_dec_priv_t *priv; /**< Algorithm private storage */
} vpx_dec_ctx_t;
#endif
/*!\brief Return the build configuration
*
* Returns a printable string containing an encoded version of
* the build configuration. This may be useful to vpx support.
*
*/
const char *vpx_dec_build_config(void) DEPRECATED;
Bankoski, et al. Informational [Page 274]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/*!\brief Return the name for a given interface
*
* Returns a human readable string for name of the given decoder
* interface.
*
* \param[in] iface Interface pointer
*
*/
const char *vpx_dec_iface_name(
vpx_dec_iface_t *iface) DEPRECATED;
/*!\brief Convert error number to printable string
*
* Returns a human readable string for the last error returned
* by the algorithm. The returned error will be one line and
* will not contain any newline characters.
*
*
* \param[in] err Error number.
*
*/
const char *vpx_dec_err_to_string(vpx_dec_err_t err) DEPRECATED;
/*!\brief Retrieve error synopsis for decoder context
*
* Returns a human readable string for the last error returned by
* the algorithm. The returned error will be one line and will
* not contain any newline characters.
*
*
* \param[in] ctx Pointer to this instance's context.
*
*/
const char *vpx_dec_error(vpx_dec_ctx_t *ctx) DEPRECATED;
/*!\brief Retrieve detailed error information for decoder context
*
* Returns a human readable string providing detailed information
* about the last error.
*
* \param[in] ctx Pointer to this instance's context.
*
Bankoski, et al. Informational [Page 275]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
* \retval NULL
* No detailed information is available.
*/
const char *vpx_dec_error_detail(vpx_dec_ctx_t *ctx) DEPRECATED;
/* REQUIRED FUNCTIONS
*
* The following functions are required to be implemented for all
* decoders. They represent the base case functionality expected
* of all decoders.
*/
/*!\brief Initialize a decoder instance
*
* Initializes a decoder context using the given interface.
* Applications should call the vpx_dec_init convenience macro
* instead of this function directly, to ensure that the ABI
* version number parameter is properly initialized.
*
* \param[in] ctx Pointer to this instance's context.
* \param[in] iface Pointer to the algorithm interface to use.
* \param[in] ver ABI version number. Must be set to
* VPX_DECODER_ABI_VERSION
* \retval #VPX_DEC_OK
* The decoder algorithm initialized.
* \retval #VPX_DEC_MEM_ERROR
* Memory allocation failed.
*/
vpx_dec_err_t vpx_dec_init_ver(
vpx_dec_ctx_t *ctx,
vpx_dec_iface_t *iface,
int ver) DEPRECATED;
#define vpx_dec_init(ctx, iface) \
vpx_dec_init_ver(ctx, iface, VPX_DECODER_ABI_VERSION)
/*!\brief Destroy a decoder instance
*
* Destroys a decoder context, freeing any associated memory
* buffers.
*
* \param[in] ctx Pointer to this instance's context
*
* \retval #VPX_DEC_OK
* The decoder algorithm initialized.
Bankoski, et al. Informational [Page 276]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
* \retval #VPX_DEC_MEM_ERROR
* Memory allocation failed.
*/
vpx_dec_err_t vpx_dec_destroy(vpx_dec_ctx_t *ctx) DEPRECATED;
/*!\brief Get the capabilities of an algorithm.
*
* Retrieves the capabilities bitfield from the algorithm's
* interface.
*
* \param[in] iface Pointer to the algorithm interface
*
*/
vpx_dec_caps_t vpx_dec_get_caps(
vpx_dec_iface_t *iface) DEPRECATED;
/*!\brief Parse stream info from a buffer
*
* Performs high level parsing of the bitstream. Construction of
* a decoder context is not necessary. Can be used to determine
* if the bitstream is of the proper format, and to extract
* information from the stream.
*
* \param[in] iface Pointer to the algorithm interface
* \param[in] data Pointer to a block of data to parse
* \param[in] data_sz Size of the data buffer
* \param[in,out] si Pointer to stream info to update. The
* size member \ref MUST be properly
* initialized, but \ref MAY be
* clobbered by the algorithm. This
* parameter \ref MAY be NULL.
*
* \retval #VPX_DEC_OK
* Bitstream is parsable and stream information updated
*/
vpx_dec_err_t vpx_dec_peek_stream_info(
vpx_dec_iface_t *iface,
const uint8_t *data,
unsigned int data_sz,
vpx_dec_stream_info_t *si) DEPRECATED;
Bankoski, et al. Informational [Page 277]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/*!\brief Return information about the current stream.
*
* Returns information about the stream that has been parsed
* during decoding.
*
* \param[in] ctx Pointer to this instance's context
* \param[in,out] si Pointer to stream info to update.
* The size member \ref MUST be properly
* initialized, but \ref MAY be clobbered
* by the algorithm. This parameter \ref
* MAY be NULL.
*
* \retval #VPX_DEC_OK
* Bitstream is parsable and stream information updated
*/
vpx_dec_err_t vpx_dec_get_stream_info(
vpx_dec_ctx_t *ctx,
vpx_dec_stream_info_t *si) DEPRECATED;
/*!\brief Control algorithm
*
* This function is used to exchange algorithm-specific data with
* the decoder instance. This can be used to implement features
* specific to a particular algorithm.
*
* This wrapper function dispatches the request to the helper
* function associated with the given ctrl_id. It tries to call
* this function transparently, but will return #VPX_DEC_ERROR if
* the request could not be dispatched.
*
* \param[in] ctx Pointer to this instance's context
* \param[in] ctrl_id Algorithm-specific control
* identifier
* \param[in,out] data Data to exchange with algorithm
* instance.
*
* \retval #VPX_DEC_OK
* The control request was processed.
* \retval #VPX_DEC_ERROR
* The control request was not processed.
* \retval #VPX_DEC_INVALID_PARAM
* The data was not valid.
*/
vpx_dec_err_t vpx_dec_control(vpx_dec_ctx_t *ctx,
int ctrl_id,
void *data) DEPRECATED;
Bankoski, et al. Informational [Page 278]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/*!\brief Decode data
*
* Processes a buffer of coded data. If the processing results
* in a new decoded frame becoming available,
* #VPX_DEC_CB_PUT_SLICE and #VPX_DEC_CB_PUT_FRAME events may be
* generated, as appropriate. Encoded data \ref MUST be passed
* in DTS (decode time stamp) order. Frames produced will always
* be in PTS (presentation time stamp) order.
*
* \param[in] ctx Pointer to this instance's context
* \param[in] data Pointer to this block of new coded
* data. If NULL, a VPX_DEC_CB_PUT_FRAME
* event is posted for the previously
* decoded frame.
* \param[in] data_sz Size of the coded data, in bytes.
* \param[in] user_priv Application-specific data to associate
* with this frame.
* \param[in] rel_pts PTS relative to the previous frame, in
* us. If unknown or unavailable, set to
* zero.
*
* \return Returns #VPX_DEC_OK if the coded data was processed
* completely and future pictures can be decoded without
* error. Otherwise, see the descriptions of the other
* error codes in ::vpx_dec_err_t for recoverability
* capabilities.
*/
vpx_dec_err_t vpx_dec_decode(
vpx_dec_ctx_t *ctx,
uint8_t *data,
unsigned int data_sz,
void *user_priv,
int rel_pts) DEPRECATED;
/*!\brief Decoded frames iterator
*
* Iterates over a list of the frames available for display. The
* iterator storage should be initialized to NULL to start the
* iteration. Iteration is complete when this function returns
* NULL.
*
* The list of available frames becomes valid upon completion of
* the vpx_dec_decode call, and remains valid until the next call
* to vpx_dec_decode.
*
* \param[in] ctx Pointer to this instance's context
* \param[in out] iter Iterator storage, initialized to NULL
Bankoski, et al. Informational [Page 279]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
*
* \return Returns a pointer to an image, if one is ready for
* display. Frames produced will always be in PTS
* (presentation time stamp) order.
*/
vpx_image_t *vpx_dec_get_frame(vpx_dec_ctx_t *ctx,
vpx_dec_iter_t *iter) DEPRECATED;
/*!\defgroup cap_put_frame Frame-Based Decoding Functions
*
* The following functions are required to be implemented for all
* decoders that advertise the VPX_DEC_CAP_PUT_FRAME capability.
* Calling these functions for codecs that don't advertise this
* capability will result in an error code being returned,
* usually VPX_DEC_ERROR @{
*/
/*!\brief put frame callback prototype
*
* This callback is invoked by the decoder to notify the
* application of the availability of decoded image data.
*/
typedef void (*vpx_dec_put_frame_cb_fn_t)(
void *user_priv,
const vpx_image_t *img);
/*!\brief Register for notification of frame completion.
*
* Registers a given function to be called when a decoded frame
* is available.
*
* \param[in] ctx Pointer to this instance's context
* \param[in] cb Pointer to the callback function
* \param[in] user_priv User's private data
*
* \retval #VPX_DEC_OK
* Callback successfully registered.
* \retval #VPX_DEC_ERROR
* Decoder context not initialized, or algorithm not capable
* of posting slice completion.
*/
vpx_dec_err_t vpx_dec_register_put_frame_cb(
vpx_dec_ctx_t *ctx,
vpx_dec_put_frame_cb_fn_t cb,
void *user_priv) DEPRECATED;
Bankoski, et al. Informational [Page 280]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/*!@} - end defgroup cap_put_frame */
/*!\defgroup cap_put_slice Slice-Based Decoding Functions
*
* The following functions are required to be implemented for all
* decoders that advertise the VPX_DEC_CAP_PUT_SLICE capability.
* Calling these functions for codecs that don't advertise this
* capability will result in an error code being returned,
* usually VPX_DEC_ERROR
* @{
*/
/*!\brief put slice callback prototype
*
* This callback is invoked by the decoder to notify the
* application of the availability of partially decoded image
* data.
*/
typedef void (*vpx_dec_put_slice_cb_fn_t)(void *user_priv,
const vpx_image_t *img,
const vpx_image_rect_t *valid,
const vpx_image_rect_t *update);
/*!\brief Register for notification of slice completion.
*
* Registers a given function to be called when a decoded slice
* is available.
*
* \param[in] ctx Pointer to this instance's context
* \param[in] cb Pointer to the callback function
* \param[in] user_priv User's private data
*
* \retval #VPX_DEC_OK
* Callback successfully registered.
* \retval #VPX_DEC_ERROR
* Decoder context not initialized, or algorithm not capable
* of posting slice completion.
*/
vpx_dec_err_t vpx_dec_register_put_slice_cb(vpx_dec_ctx_t *ctx,
vpx_dec_put_slice_cb_fn_t cb,
void *user_priv) DEPRECATED;
/*!@} - end defgroup cap_put_slice*/
Bankoski, et al. Informational [Page 281]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/*!\defgroup cap_xma External Memory Allocation Functions
*
* The following functions are required to be implemented for all
* decoders that advertise the VPX_DEC_CAP_XMA capability.
* Calling these functions for codecs that don't advertise this
* capability will result in an error code being returned,
* usually VPX_DEC_ERROR
* @{
*/
/*!\brief Memory Map Entry
*
* This structure is used to contain the properties of a memory
* segment. It is populated by the decoder in the request phase,
* and by the calling application once the requested allocation
* has been performed.
*/
#if 1
#define VPX_DEC_MEM_ZERO 0x1 /**< Segment must be zeroed by
allocation */
#define VPX_DEC_MEM_WRONLY 0x2 /**< Segment need not be
readable */
#define VPX_DEC_MEM_FAST 0x4 /**< Place in fast memory, if
available */
typedef struct vpx_codec_mmap vpx_dec_mmap_t;
#else
typedef struct vpx_dec_mmap
{
/*
* The following members are set by the codec when requesting
* a segment
*/
unsigned int id; /**< identifier for the segment's
contents */
unsigned long sz; /**< size of the segment, in bytes */
unsigned int align; /**< required alignment of the
segment, in bytes */
unsigned int flags; /**< bitfield containing segment
properties */
#define VPX_DEC_MEM_ZERO 0x1 /**< Segment must be zeroed by
allocation */
#define VPX_DEC_MEM_WRONLY 0x2 /**< Segment need not be
readable */
#define VPX_DEC_MEM_FAST 0x4 /**< Place in fast memory, if
available */
Bankoski, et al. Informational [Page 282]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/* The following members are to be filled in by the
* allocation function */
void *base; /**< pointer to the allocated
segment */
void (*dtor)(struct vpx_dec_mmap *map); /**< destructor to
call */
void *priv; /**< allocator private storage */
} vpx_dec_mmap_t;
#endif
/*!\brief Initialize a decoder instance in external allocation
* mode
*
* Initializes a decoder context using the given interface.
* Applications should call the vpx_dec_xma_init convenience
* macro instead of this function directly, to ensure that the
* ABI version number parameter is properly initialized.
*
* \param[in] ctx Pointer to this instance's context.
* \param[in] iface Pointer to the algorithm interface to
* use.
* \param[in] ver ABI version number. Must be set to
* VPX_DECODER_ABI_VERSION
* \retval #VPX_DEC_OK
* The decoder algorithm initialized.
* \retval #VPX_DEC_ERROR
* Decoder does not support XMA mode.
*/
vpx_dec_err_t vpx_dec_xma_init_ver(vpx_dec_ctx_t *ctx,
vpx_dec_iface_t *iface,
int ver) DEPRECATED;
#define vpx_dec_xma_init(ctx, iface) \
vpx_dec_xma_init_ver(ctx, iface, VPX_DECODER_ABI_VERSION)
/*!\brief Iterate over the list of segments to allocate.
*
* Iterates over a list of the segments to allocate. The
* iterator storage should be initialized to NULL to start the
* iteration. Iteration is complete when this function returns
* VPX_DEC_LIST_END. The amount of memory needed to allocate is
* dependent upon the size of the encoded stream. This means
* that the stream info structure must be known at allocation
* time. It can be populated with the vpx_dec_peek_stream_info()
* function. In cases where the stream to be decoded is not
* available at allocation time, a fixed size must be requested.
* The decoder will not be able to decode streams larger than the
* size used at allocation time.
Bankoski, et al. Informational [Page 283]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
*
* \param[in] ctx Pointer to this instance's context.
* \param[out] mmap Pointer to the memory map entry to
* populate.
* \param[in] si Pointer to the stream info.
* \param[in out] iter Iterator storage, initialized to NULL
*
* \retval #VPX_DEC_OK
* The memory map entry was populated.
* \retval #VPX_DEC_ERROR
* Decoder does not support XMA mode.
* \retval #VPX_DEC_MEM_ERROR
* Unable to determine segment size from stream info.
*/
vpx_dec_err_t vpx_dec_get_mem_map(
vpx_dec_ctx_t *ctx,
vpx_dec_mmap_t *mmap,
const vpx_dec_stream_info_t *si,
vpx_dec_iter_t *iter) DEPRECATED;
/*!\brief Identify allocated segments to decoder instance
*
* Stores a list of allocated segments in the decoder. Segments
* \ref MUST be passed in the order they are read from
* vpx_dec_get_mem_map(), but may be passed in groups of any
* size. Segments \ref MUST be set only once. The allocation
* function \ref MUST ensure that the vpx_dec_mmap_t::base member
* is non-NULL. If the segment requires cleanup handling (e.g.,
* calling free() or close()) then the vpx_dec_mmap_t::dtor
* member \ref MUST be populated.
*
* \param[in] ctx Pointer to this instance's context.
* \param[in] mmaps Pointer to the first memory map
* entry in the list.
* \param[in] num_maps Number of entries being set at this
* time
*
* \retval #VPX_DEC_OK
* The segment was stored in the decoder context.
* \retval #VPX_DEC_ERROR
* Decoder does not support XMA mode.
* \retval #VPX_DEC_MEM_ERROR
* Segment base address was not set, or segment was already
* stored.
*/
Bankoski, et al. Informational [Page 284]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
vpx_dec_err_t vpx_dec_set_mem_map(
vpx_dec_ctx_t *ctx,
vpx_dec_mmap_t *mmaps,
unsigned int num_maps) DEPRECATED;
/*!@} - end defgroup cap_xma*/
/*!@} - end defgroup decoder*/
#endif
#ifdef __cplusplus
}
#endif
---- End code block ----------------------------------------
20.22. vpx_image.c
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#include <stdlib.h>
#include <string.h>
#include "vpx/vpx_image.h"
static vpx_image_t *img_alloc_helper(vpx_image_t *img,
vpx_img_fmt_t fmt,
unsigned int d_w,
unsigned int d_h,
unsigned int stride_align,
unsigned char *img_data)
{
Bankoski, et al. Informational [Page 285]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
unsigned int h, w, s, xcs, ycs, bps;
int align;
/* Treat align==0 like align==1 */
if (!stride_align)
stride_align = 1;
/* Validate alignment (must be power of 2) */
if (stride_align & (stride_align - 1))
goto fail;
/* Get sample size for this format */
switch (fmt)
{
case VPX_IMG_FMT_RGB32:
case VPX_IMG_FMT_RGB32_LE:
case VPX_IMG_FMT_ARGB:
case VPX_IMG_FMT_ARGB_LE:
bps = 32;
break;
case VPX_IMG_FMT_RGB24:
case VPX_IMG_FMT_BGR24:
bps = 24;
break;
case VPX_IMG_FMT_RGB565:
case VPX_IMG_FMT_RGB565_LE:
case VPX_IMG_FMT_RGB555:
case VPX_IMG_FMT_RGB555_LE:
case VPX_IMG_FMT_UYVY:
case VPX_IMG_FMT_YUY2:
case VPX_IMG_FMT_YVYU:
bps = 16;
break;
case VPX_IMG_FMT_I420:
case VPX_IMG_FMT_YV12:
case VPX_IMG_FMT_VPXI420:
case VPX_IMG_FMT_VPXYV12:
bps = 12;
break;
default:
bps = 16;
break;
}
Bankoski, et al. Informational [Page 286]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/* Get chroma shift values for this format */
switch (fmt)
{
case VPX_IMG_FMT_I420:
case VPX_IMG_FMT_YV12:
case VPX_IMG_FMT_VPXI420:
case VPX_IMG_FMT_VPXYV12:
xcs = 1;
break;
default:
xcs = 0;
break;
}
switch (fmt)
{
case VPX_IMG_FMT_I420:
case VPX_IMG_FMT_YV12:
case VPX_IMG_FMT_VPXI420:
case VPX_IMG_FMT_VPXYV12:
ycs = 1;
break;
default:
ycs = 0;
break;
}
/* Calculate storage sizes given the chroma subsampling */
align = (1 << xcs) - 1;
w = (d_w + align) & ~align;
align = (1 << ycs) - 1;
h = (d_h + align) & ~align;
s = (fmt & VPX_IMG_FMT_PLANAR) ? w : bps * w / 8;
s = (s + stride_align - 1) & ~(stride_align - 1);
/* Allocate the new image */
if (!img)
{
img = (vpx_image_t *)calloc(1, sizeof(vpx_image_t));
if (!img)
goto fail;
img->self_allocd = 1;
}
Bankoski, et al. Informational [Page 287]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
else
{
memset(img, 0, sizeof(vpx_image_t));
}
img->img_data = img_data;
if (!img_data)
{
img->img_data = malloc((fmt & VPX_IMG_FMT_PLANAR) ?
h * w * bps / 8 : h * s);
img->img_data_owner = 1;
}
if (!img->img_data)
goto fail;
img->fmt = fmt;
img->w = w;
img->h = h;
img->x_chroma_shift = xcs;
img->y_chroma_shift = ycs;
img->bps = bps;
/* Calculate strides */
img->stride[VPX_PLANE_Y] = img->stride[VPX_PLANE_ALPHA] = s;
img->stride[VPX_PLANE_U] = img->stride[VPX_PLANE_V] = s >> xcs;
/* Default viewport to entire image */
if (!vpx_img_set_rect(img, 0, 0, d_w, d_h))
return img;
fail:
vpx_img_free(img);
return NULL;
}
vpx_image_t *vpx_img_alloc(vpx_image_t *img,
vpx_img_fmt_t fmt,
unsigned int d_w,
unsigned int d_h,
unsigned int stride_align)
{
return img_alloc_helper(img, fmt, d_w, d_h, stride_align, NULL);
}
Bankoski, et al. Informational [Page 288]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
vpx_image_t *vpx_img_wrap(vpx_image_t *img,
vpx_img_fmt_t fmt,
unsigned int d_w,
unsigned int d_h,
unsigned int stride_align,
unsigned char *img_data)
{
return img_alloc_helper(img, fmt, d_w, d_h, stride_align,
img_data);
}
int vpx_img_set_rect(vpx_image_t *img,
unsigned int x,
unsigned int y,
unsigned int w,
unsigned int h)
{
unsigned char *data;
if (x + w <= img->w && y + h <= img->h)
{
img->d_w = w;
img->d_h = h;
/* Calculate plane pointers */
if (!(img->fmt & VPX_IMG_FMT_PLANAR))
{
img->planes[VPX_PLANE_PACKED] =
img->img_data + x * img->bps / 8 + y *
img->stride[VPX_PLANE_PACKED];
}
else
{
data = img->img_data;
if (img->fmt & VPX_IMG_FMT_HAS_ALPHA)
{
img->planes[VPX_PLANE_ALPHA] =
data + x + y * img->stride[VPX_PLANE_ALPHA];
data += img->h * img->stride[VPX_PLANE_ALPHA];
}
img->planes[VPX_PLANE_Y] =
data + x + y * img->stride[VPX_PLANE_Y];
data += img->h * img->stride[VPX_PLANE_Y];
Bankoski, et al. Informational [Page 289]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
if (!(img->fmt & VPX_IMG_FMT_UV_FLIP))
{
img->planes[VPX_PLANE_U] = data
+ (x >> img->x_chroma_shift)
+ (y >> img->y_chroma_shift) *
img->stride[VPX_PLANE_U];
data += (img->h >> img->y_chroma_shift) *
img->stride[VPX_PLANE_U];
img->planes[VPX_PLANE_V] = data
+ (x >> img->x_chroma_shift)
+ (y >> img->y_chroma_shift) *
img->stride[VPX_PLANE_V];
}
else
{
img->planes[VPX_PLANE_V] = data
+ (x >> img->x_chroma_shift)
+ (y >> img->y_chroma_shift) *
img->stride[VPX_PLANE_V];
data += (img->h >> img->y_chroma_shift) *
img->stride[VPX_PLANE_V];
img->planes[VPX_PLANE_U] = data
+ (x >> img->x_chroma_shift)
+ (y >> img->y_chroma_shift) *
img->stride[VPX_PLANE_U];
}
}
return 0;
}
return -1;
}
void vpx_img_flip(vpx_image_t *img)
{
/* Note: In the calculation pointer adjustment calculation, we
* want the rhs to be promoted to a signed type. Section 6.3.1.8
* of the ISO C99 standard [ISO-C99] indicates that if the
* adjustment parameter is unsigned, the stride parameter will be
* promoted to unsigned, causing errors when the lhs is a larger
* type than the rhs.
*/
img->planes[VPX_PLANE_Y] += (signed)
(img->d_h - 1) * img->stride[VPX_PLANE_Y];
img->stride[VPX_PLANE_Y] = -img->stride[VPX_PLANE_Y];
Bankoski, et al. Informational [Page 290]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
img->planes[VPX_PLANE_U] += (signed)
((img->d_h >> img->y_chroma_shift) - 1)
* img->stride[VPX_PLANE_U];
img->stride[VPX_PLANE_U] = -img->stride[VPX_PLANE_U];
img->planes[VPX_PLANE_V] += (signed)
((img->d_h >> img->y_chroma_shift) - 1) *
img->stride[VPX_PLANE_V];
img->stride[VPX_PLANE_V] = -img->stride[VPX_PLANE_V];
img->planes[VPX_PLANE_ALPHA] += (signed)
(img->d_h - 1) * img->stride[VPX_PLANE_ALPHA];
img->stride[VPX_PLANE_ALPHA] = -img->stride[VPX_PLANE_ALPHA];
}
void vpx_img_free(vpx_image_t *img)
{
if (img)
{
if (img->img_data && img->img_data_owner)
free(img->img_data);
if (img->self_allocd)
free(img);
}
}
---- End code block ----------------------------------------
20.23. vpx_image.h
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
/*!\file
* \brief Describes the vpx image descriptor and associated
* operations
*
*/
Bankoski, et al. Informational [Page 291]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
#ifdef __cplusplus
extern "C" {
#endif
#ifndef VPX_IMAGE_H
#define VPX_IMAGE_H
/*!\brief Current ABI version number
*
* \internal
* If this file is altered in any way that changes the ABI, this
* value must be bumped. Examples include, but are not limited
* to, changing types, removing or reassigning enums,
* adding/removing/rearranging fields to structures
*/
#define VPX_IMAGE_ABI_VERSION (1) /**<\hideinitializer*/
#define VPX_IMG_FMT_PLANAR 0x100 /**< Image is a planar
format */
#define VPX_IMG_FMT_UV_FLIP 0x200 /**< V plane precedes U plane
in memory */
#define VPX_IMG_FMT_HAS_ALPHA 0x400 /**< Image has an alpha channel
component */
/*!\brief List of supported image formats */
typedef enum vpx_img_fmt {
VPX_IMG_FMT_NONE,
VPX_IMG_FMT_RGB24, /**< 24 bit per pixel packed RGB */
VPX_IMG_FMT_RGB32, /**< 32 bit per pixel packed 0RGB */
VPX_IMG_FMT_RGB565, /**< 16 bit per pixel, 565 */
VPX_IMGFMT_RGB555, /**< 16 bit per pixel, 555 */
VPX_IMG_FMT_UYVY, /**< UYVY packed YUV */
VPX_IMG_FMT_YUY2, /**< YUYV packed YUV */
VPX_IMG_FMT_YVYU, /**< YVYU packed YUV */
VPX_IMG_FMT_BGR24, /**< 24 bit per pixel packed BGR */
VPX_IMG_FMT_RGB32_LE, /**< 32 bit packed BGR0 */
VPX_IMG_FMT_ARGB, /**< 32 bit packed ARGB, alpha=255 */
VPX_IMG_FMT_ARGB_LE, /**< 32 bit packed BGRA, alpha=255 */
VPX_IMG_FMT_RGB565_LE, /**< 16 bit per pixel,
gggbbbbb rrrrrggg */
VPX_IMG_FMT_RGB555_LE, /**< 16 bit per pixel,
gggbbbbb 0rrrrrgg */
VPX_IMG_FMT_YV12 = VPX_IMG_FMT_PLANAR |
VPX_IMG_FMT_UV_FLIP | 1, /**< planar YVU */
VPX_IMG_FMT_I420 = VPX_IMG_FMT_PLANAR | 2,
Bankoski, et al. Informational [Page 292]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
VPX_IMG_FMT_VPXYV12 = VPX_IMG_FMT_PLANAR |
VPX_IMG_FMT_UV_FLIP | 3, /** < planar 4:2:0 format with
vpx color space */
VPX_IMG_FMT_VPXI420 = VPX_IMG_FMT_PLANAR | 4 /** < planar
4:2:0 format with vpx color space */
}
vpx_img_fmt_t; /**< alias for enum vpx_img_fmt */
#if !defined(VPX_CODEC_DISABLE_COMPAT) || !VPX_CODEC_DISABLE_COMPAT
/** \deprecated Use #VPX_IMG_FMT_PLANAR */
#define IMG_FMT_PLANAR VPX_IMG_FMT_PLANAR
/** \deprecated Use #VPX_IMG_FMT_UV_FLIP */
#define IMG_FMT_UV_FLIP VPX_IMG_FMT_UV_FLIP
/** \deprecated Use #VPX_IMG_FMT_HAS_ALPHA */
#define IMG_FMT_HAS_ALPHA VPX_IMG_FMT_HAS_ALPHA
/*!\brief Deprecated list of supported image formats
* \deprecated New code should use #vpx_img_fmt
*/
#define img_fmt vpx_img_fmt
/*!\brief alias for enum img_fmt.
* \deprecated New code should use #vpx_img_fmt_t
*/
#define img_fmt_t vpx_img_fmt_t
/** \deprecated Use #VPX_IMG_FMT_NONE */
#define IMG_FMT_NONE VPX_IMG_FMT_NONE
/** \deprecated Use #VPX_IMG_FMT_RGB24 */
#define IMG_FMT_RGB24 VPX_IMG_FMT_RGB24
/** \deprecated Use #VPX_IMG_FMT_RGB32 */
#define IMG_FMT_RGB32 VPX_IMG_FMT_RGB32
/** \deprecated Use #VPX_IMG_FMT_RGB565 */
#define IMG_FMT_RGB565 VPX_IMG_FMT_RGB565
/** \deprecated Use #VPX_IMG_FMT_RGB555 */
#define IMG_FMT_RGB555 VPX_IMG_FMT_RGB555
/** \deprecated Use #VPX_IMG_FMT_UYVY */
#define IMG_FMT_UYVY VPX_IMG_FMT_UYVY
/** \deprecated Use #VPX_IMG_FMT_YUY2 */
#define IMG_FMT_YUY2 VPX_IMG_FMT_YUY2
/** \deprecated Use #VPX_IMG_FMT_YVYU */
#define IMG_FMT_YVYU VPX_IMG_FMT_YVYU
/** \deprecated Use #VPX_IMG_FMT_BGR24 */
#define IMG_FMT_BGR24 VPX_IMG_FMT_BGR24
/**< \deprecated Use #VPX_IMG_FMT_RGB32_LE */
#define IMG_FMT_RGB32_LE VPX_IMG_FMT_RGB32_LE
/** \deprecated Use #VPX_IMG_FMT_ARGB */
#define IMG_FMT_ARGB VPX_IMG_FMT_ARGB
Bankoski, et al. Informational [Page 293]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
/** \deprecated Use #VPX_IMG_FMT_ARGB_LE */
#define IMG_FMT_ARGB_LE VPX_IMG_FMT_ARGB_LE
/** \deprecated Use #VPX_IMG_FMT_RGB565_LE */
#define IMG_FMT_RGB565_LE VPX_IMG_FMT_RGB565_LE
/** \deprecated Use #VPX_IMG_FMT_RGB555_LE */
#define IMG_FMT_RGB555_LE VPX_IMG_FMT_RGB555_LE
/** \deprecated Use #VPX_IMG_FMT_YV12 */
#define IMG_FMT_YV12 VPX_IMG_FMT_YV12
/** \deprecated Use #VPX_IMG_FMT_I420 */
#define IMG_FMT_I420 VPX_IMG_FMT_I420
/** \deprecated Use #VPX_IMG_FMT_VPXYV12 */
#define IMG_FMT_VPXYV12 VPX_IMG_FMT_VPXYV12
/** \deprecated Use #VPX_IMG_FMT_VPXI420 */
#define IMG_FMT_VPXI420 VPX_IMG_FMT_VPXI420
#endif /* VPX_CODEC_DISABLE_COMPAT */
/**\brief Image Descriptor */
typedef struct vpx_image
{
vpx_img_fmt_t fmt; /**< Image Format */
/* Image storage dimensions */
unsigned int w; /**< Stored image width */
unsigned int h; /**< Stored image height */
/* Image display dimensions */
unsigned int d_w; /**< Displayed image width */
unsigned int d_h; /**< Displayed image height */
/* Chroma subsampling info */
unsigned int x_chroma_shift; /**< subsampling order, X */
unsigned int y_chroma_shift; /**< subsampling order, Y */
/* Image data pointers. */
#define VPX_PLANE_PACKED 0 /**< To be used for all packed formats */
#define VPX_PLANE_Y 0 /**< Y (Luminance) plane */
#define VPX_PLANE_U 1 /**< U (Chroma) plane */
#define VPX_PLANE_V 2 /**< V (Chroma) plane */
#define VPX_PLANE_ALPHA 3 /**< A (Transparency) plane */
#if !defined(VPX_CODEC_DISABLE_COMPAT) || !VPX_CODEC_DISABLE_COMPAT
#define PLANE_PACKED VPX_PLANE_PACKED
#define PLANE_Y VPX_PLANE_Y
#define PLANE_U VPX_PLANE_U
#define PLANE_V VPX_PLANE_V
#define PLANE_ALPHA VPX_PLANE_ALPHA
#endif
Bankoski, et al. Informational [Page 294]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
unsigned char *planes[4]; /**< pointer to the top-left pixel
q for each plane */
int stride[4]; /**< stride between rows for each plane */
int bps; /**< bits per sample (for packed formats) */
/* The following member may be set by the application to
* associate data with this image.
*/
void *user_priv; /**< may be set by the application to
associate data with this image. */
/* The following members should be treated as private. */
unsigned char *img_data; /**< private */
int img_data_owner; /**< private */
int self_allocd; /**< private */
} vpx_image_t; /**< alias for struct vpx_image */
/**\brief Representation of a rectangle on a surface */
typedef struct vpx_image_rect
{
unsigned int x; /**< leftmost column */
unsigned int y; /**< topmost row */
unsigned int w; /**< width */
unsigned int h; /**< height */
} vpx_image_rect_t; /**< alias for struct vpx_image_rect */
/*!\brief Open a descriptor, allocating storage for the
* underlying image
*
* Returns a descriptor for storing an image of the given format.
* The storage for the descriptor is allocated on the heap.
*
* \param[in] img Pointer to storage for descriptor.
* If this parameter is NULL, the storage
* for the descriptor will be allocated
* on the heap.
* \param[in] fmt Format for the image
* \param[in] d_w Width of the image
* \param[in] d_h Height of the image
* \param[in] align Alignment, in bytes, of each row in
* the image.
*
* \return Returns a pointer to the initialized image descriptor.
* If the img parameter is non-null, the value of the img
* parameter will be returned.
*/
Bankoski, et al. Informational [Page 295]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
vpx_image_t *vpx_img_alloc(vpx_image_t *img,
vpx_img_fmt_t fmt,
unsigned int d_w,
unsigned int d_h,
unsigned int align);
/*!\brief Open a descriptor, using existing storage for the
* underlying image
*
* Returns a descriptor for storing an image of the given format.
* The storage for descriptor has been allocated elsewhere, and a
* descriptor is desired to "wrap" that storage.
*
* \param[in] img Pointer to storage for descriptor.
* If this parameter is NULL, the storage
* for the descriptor will be
* allocated on the heap.
* \param[in] fmt Format for the image
* \param[in] d_w Width of the image
* \param[in] d_h Height of the image
* \param[in] align Alignment, in bytes, of each row in
* the image.
* \param[in] img_data Storage to use for the image
*
* \return Returns a pointer to the initialized image descriptor.
* If the img parameter is non-null, the value of the img
* parameter will be returned.
*/
vpx_image_t *vpx_img_wrap(vpx_image_t *img,
vpx_img_fmt_t fmt,
unsigned int d_w,
unsigned int d_h,
unsigned int align,
unsigned char *img_data);
/*!\brief Set the rectangle identifying the displayed portion of
* the image
*
* Updates the displayed rectangle (aka viewport) on the image
* surface to match the specified coordinates and size.
*
* \param[in] img Image descriptor
* \param[in] x leftmost column
* \param[in] y topmost row
* \param[in] w width
* \param[in] h height
*
Bankoski, et al. Informational [Page 296]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
* \return 0 if the requested rectangle is valid, non-zero
* otherwise.
*/
int vpx_img_set_rect(vpx_image_t *img,
unsigned int x,
unsigned int y,
unsigned int w,
unsigned int h);
/*!\brief Flip the image vertically (top for bottom)
*
* Adjusts the image descriptor's pointers and strides to make
* the image be referenced upside-down.
*
* \param[in] img Image descriptor
*/
void vpx_img_flip(vpx_image_t *img);
/*!\brief Close an image descriptor
*
* Frees all allocated storage associated with an image
* descriptor.
*
* \param[in] img Image descriptor
*/
void vpx_img_free(vpx_image_t *img);
#endif
#ifdef __cplusplus
}
#endif
---- End code block ----------------------------------------
Bankoski, et al. Informational [Page 297]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
20.24. vpx_integer.h
---- Begin code block --------------------------------------
/*
* Copyright (c) 2010, 2011, Google Inc. All rights reserved.
*
* Use of this source code is governed by a BSD-style license
* that can be found in the LICENSE file in the root of the source
* tree. An additional intellectual property rights grant can be
* found in the file PATENTS. All contributing project authors may
* be found in the AUTHORS file in the root of the source tree.
*/
#ifndef VPX_INTEGER_H
#define VPX_INTEGER_H
/* get ptrdiff_t, size_t, wchar_t, NULL */
#include <stddef.h>
#if defined(_MSC_VER) || defined(VPX_EMULATE_INTTYPES)
typedef signed char int8_t;
typedef signed short int16_t;
typedef signed int int32_t;
typedef unsigned char uint8_t;
typedef unsigned short uint16_t;
typedef unsigned int uint32_t;
#if defined(_MSC_VER)
typedef signed __int64 int64_t;
typedef unsigned __int64 uint64_t;
#define PRId64 "I64d"
#endif
#ifdef HAVE_ARMV6
typedef unsigned int int_fast16_t;
#else
typedef signed short int_fast16_t;
#endif
typedef signed char int_fast8_t;
typedef unsigned char uint_fast8_t;
#ifndef _UINTPTR_T_DEFINED
typedef unsigned int uintptr_t;
#endif
Bankoski, et al. Informational [Page 298]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
#else
/* Most platforms have the C99 standard integer types. */
#if defined(__cplusplus) && !defined(__STDC_FORMAT_MACROS)
#define __STDC_FORMAT_MACROS
#endif
#include <stdint.h>
#include <inttypes.h>
#endif
#endif
---- End code block ----------------------------------------
20.25. AUTHORS File
Aaron Watry <awatry@gmail.com>
Adrian Grange <agrange@google.com>
Alex Converse <alex.converse@gmail.com>
Andoni Morales Alastruey <ylatuya@gmail.com>
Andres Mejia <mcitadel@gmail.com>
Attila Nagy <attilanagy@google.com>
Fabio Pedretti <fabio.ped@libero.it>
Frank Galligan <fgalligan@google.com>
Fredrik Soederquist <fs@opera.com>
Fritz Koenig <frkoenig@google.com>
Gaute Strokkenes <gaute.strokkenes@broadcom.com>
Giuseppe Scrivano <gscrivano@gnu.org>
Guillermo Ballester Valor <gbvalor@gmail.com>
Henrik Lundin <hlundin@google.com>
James Berry <jamesberry@google.com>
Bankoski, et al. Informational [Page 299]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
James Zern <jzern@google.com>
Jan Kratochvil <jan.kratochvil@redhat.com>
Jeff Muizelaar <jmuizelaar@mozilla.com>
Jim Bankoski <jimbankoski@google.com>
Johann Koenig <johannkoenig@google.com>
John Koleszar <jkoleszar@google.com>
Justin Clift <justin@salasaga.org>
Justin Lebar <justin.lebar@gmail.com>
Luca Barbato <lu_zero@gentoo.org>
Makoto Kato <makoto.kt@gmail.com>
Martin Ettl <ettl.martin78@googlemail.com>
Michael Kohler <michaelkohler@live.com>
Mikhal Shemer <mikhal@google.com>
Pascal Massimino <pascal.massimino@gmail.com>
Patrik Westin <patrik.westin@gmail.com>
Paul Wilkins <paulwilkins@google.com>
Pavol Rusnak <stick@gk2.sk>
Philip Jaegenstedt <philipj@opera.com>
Scott LaVarnway <slavarnway@google.com>
Tero Rintaluoma <teror@google.com>
Timothy B. Terriberry <tterribe@xiph.org>
Tom Finegan <tomfinegan@google.com>
Yaowu Xu <yaowu@google.com>
Yunqing Wang <yunqingwang@google.com>
Bankoski, et al. Informational [Page 300]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
Google Inc.
The Mozilla Foundation
The Xiph.Org Foundation
20.26. LICENSE
Copyright (c) 2010, 2011, Google Inc. All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
o Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
o Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in
the documentation and/or other materials provided with the
distribution.
o Neither the name of Google nor the names of its contributors may
be used to endorse or promote products derived from this software
without specific prior written permission.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY
WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
POSSIBILITY OF SUCH DAMAGE.
Bankoski, et al. Informational [Page 301]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
20.27. PATENTS
Additional IP Rights Grant (Patents)
"This implementation" means the copyrightable works distributed by
Google as part of the WebM Project.
Google hereby grants to you a perpetual, worldwide, non-exclusive,
no-charge, royalty-free, irrevocable (except as stated in this
section) patent license to make, have made, use, offer to sell, sell,
import, transfer, and otherwise run, modify and propagate the
contents of this implementation of VP8, where such license applies
only to those patent claims, both currently owned by Google and
acquired in the future, licensable by Google that are necessarily
infringed by this implementation of VP8. This grant does not include
claims that would be infringed only as a consequence of further
modification of this implementation. If you or your agent or
exclusive licensee institute or order or agree to the institution of
patent litigation against any entity (including a cross-claim or
counterclaim in a lawsuit) alleging that this implementation of VP8
or any code incorporated within this implementation of VP8
constitutes direct or contributory patent infringement, or inducement
of patent infringement, then any patent rights granted to you under
this License for this implementation of VP8 shall terminate as of the
date such litigation is filed.
21. Security Considerations
A VP8 decoder should take appropriate security considerations into
account, as outlined in [RFC4732] and [RFC3552]. It is extremely
important that a decoder be robust against malicious payloads.
Malicious payloads must not cause the decoder to overrun its
allocated memory or to consume inordinate resources. Although
encoder issues are typically rarer, the same applies to an encoder.
Malicious stream data must not cause the encoder to misbehave, as
this might allow an attacker access to transcoding gateways.
Bankoski, et al. Informational [Page 302]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
22. References
22.1. Normative Reference
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
22.2. Informative References
[Bell] Bell, T., Cleary, J., and I. Witten, "Text Compression",
1990.
[ISO-C99] International Organization for Standardization,
"Information technology -- Programming languages -- C",
ISO/IEC 9899:1999, 1999.
[ITU-R_BT.601]
International Telecommunication Union, "ITU BT.601-7:
Studio encoding parameters of digital television for
standard 4:3 and wide screen 16:9 aspect ratios",
March 2011.
[Kernighan] Kernighan, B. and D. Ritchie, "The C Programming Language
(2nd edition)", April 1988.
[Loeffler] Loeffler, C., Ligtenberg , A., and G. Moschytz,
"Practical Fast 1-D DCT Algorithms with 11
Multiplications", May 1989.
[RFC3552] Rescorla, E. and B. Korver, "Guidelines for Writing RFC
Text on Security Considerations", BCP 72, RFC 3552,
July 2003.
[RFC4732] Handley, M., Ed., Rescorla, E., Ed., and IAB, "Internet
Denial-of-Service Considerations", RFC 4732,
December 2006.
[Shannon] Shannon, C., "A Mathematical Theory of Communication",
Bell System Technical Journal Vol. 27, pp. 379-423 and
623-656, July and October 1948.
Bankoski, et al. Informational [Page 303]
RFC 6386 VP8 Data Format and Decoding Guide November 2011
Authors' Addresses
James Bankoski
Google Inc.
EMail: jimbankoski@google.com
John Koleszar
Google Inc.
EMail: jkoleszar@google.com
Lou Quillio
Google Inc.
EMail: louquillio@google.com
Janne Salonen
Google Inc.
EMail: jsalonen@google.com
Paul Wilkins
Google Inc.
EMail: paulwilkins@google.com
Yaowu Xu
Google Inc.
EMail: yaowu@google.com
Bankoski, et al. Informational [Page 304]