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

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))

Perfect answer above. I use it together with find to add all FLAC files in a subtree to iTunes with this command

find . -name "*.flac" -exec ffmpeg -i {} -ab 160k -map_metadata 0 -id3v2_version 3 {}.mp3 \;

To automatically add the resulting files to iTunes, get the iTunes import directory with

find ~/Music/ -name "Automatically Add*"

result e.g.

/Users/sir/Music//iTunes/iTunes Media/Automatically Add to iTunes.localized

Then run e.g.

find . -name "*.mp3" -exec mv {} "/Users/sir/Music//iTunes/iTunes Media/Automatically Add to iTunes.localized/" \;

To automatically add all the converted tracks to iTunes.

If you want to save a little space, try the recommendation of hydrogenaud.io:

Very high quality: HiFi, home, or quiet listening, with best file size -V0 (~245 kbps), -V1 (~225 kbps), -V2 (~190 kbps) or -V3 (~175 kbps) are recommended. These VBR settings will normally produce transparent results. Audible differences between these presets may exist, but are rare.

Source: http://wiki.hydrogenaud.io/index.php?title=LAME

If you want use this option in ffmpeg, you should use the -q:a 0 alias.

Control quality with -qscale:a (or the alias -q:a). Values are encoder specific, so for libmp3lame the range is 0-9 where a lower value is a higher quality. 0-3 will normally produce transparent results, 4 (default) should be close to perceptual transparency, and 6 produces an "acceptable" quality. The option -qscale:a is mapped to the -V option in the standalone lame command-line interface tool.

Source: https://trac.ffmpeg.org/wiki/Encode/MP3

If you want ID3v1 metatags too, you should add the -write_id3v1 1 parameter.

So my final command is:

ffmpeg.exe -y -i input.flac -codec:a libmp3lame -q:a 0 -map_metadata 0 -id3v2_version 3 -write_id3v1 1 output.mp3

The following command keeps high quality on .mp3 (320 kbps), and metadata from .flac file are converted to ID3v2 format, which can be included in .mp3 files:

ffmpeg -i input.flac -ab 320k -map_metadata 0 -id3v2_version 3 output.mp3