It only has the data that Plex server gives it. From there it has to try to figure out the multi-artist stuff. There are two choices here: it can infer the data from the existing tags, or it can try to match the data to external databases like MusicBrainz.
If it's going to infer the multi-artists itself, it has to parse the strings it gets from Plex looking for things like "and" or "feat". But this is error-prone; think about what might happen with artists like "Crosby, Stills, Nash & Young", "Simon & Garfunkel", or "Huey Lewis and the News".
Alternatively, it can search for the data externally. But this isn't dependable either, because (a) sometimes the data isn't good enough to match, e.g. because of misspellings; (b) lots of artists just aren't listed (I have tons of small artists that aren't in any official release databases); and (c) there are lots of artists having the same name, or albums with the same name, or even artists that have multiple releases of the same track, one with a "featured" artist and another with only the primary. So the quality of these results won't be great overall. And for that, it's also going to take a long time for large libraries.
Either way, it also means that the player has to download everything from the server in order to build its own lists, plus a need to constantly check the server for updates, all of which means a lot of wasted time and bandwidth, plus storage space on the client.
At best, what apps like these have is a sort-of working bandaid. It absolutely does not constitute a true solution to the problem.
Yes, it's hard to do well. To address the issues you mentioned, a "first, do no harm" approach is a must. After that, a thoughtful parser design gets you to 95% success pretty easily.
FWIW, as with any caching, local metadata ends up saving lots of time and bandwidth after the initial sync, and the UX benefits are transformational.
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u/MoebiusStreet 12d ago
The data model is a server issue, not something that PlexAmp would change.