For the users that chose to use their own tags instead of internet fetched ones, I suggest that Plex should support more “special” tags from the files. I suggest to support MusicBrainz tags because they are supposed to be a standard for music tagging.
Most people use the software “MusicBrainz Picard” to tag their files if they use MusicBrainz and here is a list of its tag mappings through various formats: https://picard.musicbrainz.org/docs/mappings/
The most obvious example here is “Record Label” because you already support this as a filter in the UI, but currently Plex can not read the correct tag field to populate this info if the user wants his own tags used. MusicBrainz have this information in the vast majority of cases so it would prove useful. Also the tag field is a standard one, so it would also benefit users who input the label manually of from other sources/applications.
Also of importance is the “Date” field which Plex uses but (at least with ID3v2.3 which I tested) is unable to properly read if stored with MusicBrainz standard. Plex reads only “year” but puts 01-01 as date. So if a user has only Musicbrainz tags, his entire library has albums released 01-01. Standards for mp3 vary here, but I would say it would be best to support the MusicBrainz way of doing this, partly because the application “Mp3tag” (very popular tagging program) uses the same method afaik, and also partly because MusicBrainz have this information in the vast majority of cases (hence Picard will write it) so it is not just overly obsessive people that has this in the tags.
It would also be nice to support “Release Type”. Picard writes this in 99% of cases. As it is now in Plex, all types gets thrown together, but if this tag gets supported it would be possible to visually separate Albums, EPs, Singles, Remix albums etc.
Additionally, it would be fun to have some fluff supported as well. Such as Composer, Lyricist, who performed what instrument, arranger, producer, language of the lyrics etc. It would be really good for filtering. I guess this is not overly important as such, because it is only in a minority of cases that MusicBrainz has this information available anyway. And the tags involved are not always standardized (some are MusicBrainz exclusive and does not exist in mp3 specifications). But it would stil be nice to have, if development time allows it. Fields which are standardized (and which I personally think would be most relevant to support) are Composer and Lyricist.
Generally it could also be an idea to (optionally) display the “Comment” field for a track somehow, because a user might have put relevant things in there. Like a personal note about a song. Note also that via the Picard software it is possible to automatically put certain extra information in that field which does not fit elsewhere (such as the fact that the song is a cover, and who it was originally performed by). This is done via plugins however and overall I guess this is not something everyone would care for. But again, if time allows, it would be nice to have.
I also think it’s important to have equal support for id3v2.3 as with id3v2.4 if implementing more tags because id3v2.3 is still used by many devices today, legacy or not.
Finally, if this looks like “too much”, I would argue that it is not, because a user who goes into the advanced section just to check “use my own tags” probably expects that most of his tags would be put to use. And it is not uncommon for desktop music players to show various special tags such as the “comment”, “composer”, “lyricst” or some custom MusicBrainz tags. Hence if this is supported on Plex as well, the change for such people would not be so big.
