petitminion Am I forgetting something ?
Yes, the artist credit. At the moment it's crucial to retrieve and use the standard artist spelling as provided in the MusicBrainz entry for the artist, as it will be used by all releases and tracks with that artist MBID. Keeping the artist name provided by the tags will result in a non-standard spelling being used by all releases, and in each artist's category. Getting the artist credit and displaying it in the UI should be considered extra functionality, though people will definitely welcome it.
And since you'll do such huge changes to the database structure, might as well do it now I guess?
heyarne can you provide links to some docs on how these tags are actually set, or is this all folklore & arcane knowledge gained reading the picard source code?
It's just a bunch of painful experience. I initially used beets for managing my music library but their database structure and tag parser has THIS EXACT SAME ISSUE which was very painful to find out months down the line after troubleshooting it endlessly.
Picard does have docs for this though.
These tags can be retrieved if you use a plugin to enable the functionality. And it's a nice touch that the artist variables are provided by a built-in plugin too.
This is the starting page for scripting. It is based on the format used by foobar2000. It's easy to use, though not so much if you're computer illiterate I guess.
You don't seem to be, but since I already learned how this works more or less I could provide you with a script that does the work you'd otherwise use the API for; and yet still, as you said it's useless if you have to tell the user to do it manually.
And it doesn't do concatenation processing either so there's that.
EDIT: At some point I forgot to say: Picard stores in the tags whether the release is a compilation. This shouldn't be figured out by checking for the Various Artist string or its associated MBID as some compilations have an album artist stored in MusicBrainz.
Since I'm bringing this up: the information stored will tell you in full detail what the release type is. Remix album, compilation remix, broadcast demo, remix single, live ep, etc. It even tells you if a single or EP belongs to an album or a compilation and such, if there's a non-credited artist or label who does the compilation as well. I don't know how much of this information is exposed through the API or how much you wanna store on the Funkwhale database, but for future reference I'm putting this out there.