Convert .flac to .mp3 with ffmpeg, keeping all metadata

Question

How can I convert .flac to .mp3 with ffmpeg, keeping all metadata (that is converting Vorbis comment in .flac files to ID3v2 metadata of .mp3)?

Answer 1

One-liner to convert all .flac files to .mp3 in a single directory, keeping most metadata:

for file in *.flac; do ffmpeg -i $file -q:a 0 ${file:r}.mp3; done

(Note: ${file:r} removes the extension of the given filepath)

Answer 2

I was testing the following command to convert infile.flac file to outfile.mp3:

ffmpeg  -i infile.flac  -q:a 0  outfile.mp3

As of Ubuntu 16.04, the above command seems to copy (most of? all of?) the metadata.

-q:a 0 tells ffmpeg to use the highest quality VBR.

However, ffmpeg was transcoding my album art from jpeg to png, which increased the size of the cover art.

Stream mapping:
  Stream #0:1 -> #0:0 (mjpeg (native) -> png (native))
  Stream #0:0 -> #0:1 (flac (native) -> mp3 (libmp3lame))

(I guess the above conversion sort of makes sense given how ffmpeg works.)

After some digging, I found the -c:v copy option, which specifies that the video stream should be copied, rather than transcoded. The full command is:

ffmpeg  -i infile.flac  -c:v copy  -q:a 0  outfile.mp3

The above command results in:

Stream mapping:
  Stream #0:1 -> #0:0 (copy)
  Stream #0:0 -> #0:1 (flac (native) -> mp3 (libmp3lame))