`ffmpeg` will keep all the metadata as ID3v2 but won’t copy to ID3v1. I don’t care. `-q:a 0` says to use the best variable bit rate (VBR). `-c:v copy` says to just copy video, ie. JPEG covers are not turned into PNG.
find . -name "*.flac" -exec ffmpeg -i {} -q:a 0 -c:v copy {}.mp3 \;
Names now end in `.flac.mp3`. Assuming you have `brew install rename`, this should be easy:
rename 's/\.flac\.mp3/.mp3/' *.flac.mp3
#Music