Beets should allow tagging multiple artists and albumartists in files that use Vorbis comments

[afontenot]

Vorbis comments are used for FLAC, Vorbis, and Opus files. They are a much better system than the ID3 tags used by MP3s. In particular, they support tagging multiple artists on a track or album by using multiple tags. In fact this is the way of tagging multiple artists that is explicitly endorsed by the creators of Vorbis.

The MusicBrainz source used by Beets to tag files also keeps track of artists separately, instead of as a single tag. See this JSON file for one collaboration album.

Unfortunately, for both artists and albumartists, Beets squashes the tag into a single one, even for files that support Vorbis comments. This behavior is mirrored by the Picard tagger.

How can I get Beets to tag files in this way? What I'd like to see, more specifically:

ALBUMARTIST=Floating Points
ALBUMARTIST=Pharoah Sanders
ALBUMARTIST=London Symphony Orchestra
ALBUMARTIST_CREDIT=Floating Points, Pharoah Sanders & The London Symphony Orchestra

I'm not totally sold on the last one, if someone has an idea for a better standard way to present the artists as credited on the cover.

I'd like to do this internally in Beets if at all possible, because I use mbsync to keep the files up to date. Would functionality like this be considered as a feature request? Or would I need to create a plugin?

[afontenot]

Some interesting links:

• blocking issue: Add support for multi-valued tags #505
• missing feature that would enable workarounds: mbsync: Don't overwrite genres from MusicBrainz while the underlying library does not support them #4071
• Picard documentation for related features: https://picard-docs.musicbrainz.org/en/variables/variables_basic.html
• Picard open bug for implementation of the other half of the feature, with related discussion: https://tickets.metabrainz.org/browse/PICARD-700

It was not at all obvious to me from the documentation that Picard actually supports this partially out of the box. In the GUI, it displays what the documentation calls a "multi-value" as a string with a delimiter (usually apostrophe). When you actually save the file, however, multi-values are written out as instances of a single tag, if the underlying format supports it.

Picard's way of implementing my idea / request is by using the original albumartist tag as basically albumartist_credit as I conceived it, and introducing a new tag, albumartists (notice the plural) which can appear in multiple instances and contains the names of individual artists. And similarly with the artists tag.

The following Picard tagger script will get you the rest of the way there:

$setmulti(albumartists,%_albumartists%)

Apparently this is a quasi-standard used by several players, which is a good enough reason for me to use it IMO. (In any case the players I use are flexible enough for me to have them use these alternative tags.)

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I'm concerned about losing the ability to use mbsync, however, and I'd much prefer to use Beets because all my music is on a headless server which makes a terminal-based tool much easier.

Any thoughts or advice anyone has are appreciated!