Having multiple transcoded mp3 versions, and keep it synced

[tomribbens]

I'd like to have the following setup, but can't seem to figure out how to achieve it:

I mainly have FLAC copies of my music. I'd like it to maintain three different mp3 copies of that music: 320kbps, V0 and V2, all in seperate trees.

When something gets updated on musicbrainz, and it gets propagated to my own library (through mbsync for example), I'd like the converted copies also to get their metadata updated.

I know of beets-alternatives, but unless I don't understand how to configure it and the convert plugin, it's only possible to have a single convert command for mp3, and so I can't get the three different versions easily?

[Hikari-Tsai]

The convert plugin can have multiple named formats even when they all use the .mp3 extension. Give each preset a unique key and set extension: mp3:

plugins: convert

convert:
  refresh: yes
  formats:
    mp3-320:
      command: ffmpeg -i $source -y -vn -codec:a libmp3lame -b:a 320k $dest
      extension: mp3
    mp3-v0:
      command: ffmpeg -i $source -y -vn -codec:a libmp3lame -q:a 0 $dest
      extension: mp3
    mp3-v2:
      command: ffmpeg -i $source -y -vn -codec:a libmp3lame -q:a 2 $dest
      extension: mp3

Then export each tree separately:

beet convert -f mp3-320 -d /music/mp3-320
beet convert -f mp3-v0   -d /music/mp3-v0
beet convert -f mp3-v2   -d /music/mp3-v2

After mbsync, make sure the changed metadata is written to the source files (for example, use the plugin's write option or run beet write <query>). That updates the source modification time. Re-running the three commands with refresh: yes then regenerates destination files whose source is newer.

I would keep the FLAC database as the canonical library and treat all three MP3 trees as reproducible exports; three separately managed beets libraries would make synchronization harder.