I have some classical music in my library. I tagged ensembles, conductors, guest musicians in the artist field divided by an "/" Example "Berliner Philharmoniker / Nigel Kennedy". If there is a unifying element in the album like an ensemble for example, I put that in the albumartist field. Composers are in the composers field. I did that basically for scraping reasons. The artists in the artist fields get scraped. A composer, special guest, conductor would not be scraped by kodi. I did the tagging manually through mp3tag. It is a kind of an okay-ish solution for me.
I follow the proposals for changes with great interest. In the thread in the dev forum evilhamster stated that the whole situation is a mess. To find out what kind of mess I downloaded a classical album from amazon today. I'd say amazon is a big enough player in the market, so that some users might have music bought and tagged through amazon on their drives. I wanted to see how the files are tagged and have a real user's life example of what will likely be thrown at kodi to "make the best out of it".
To be precise I bought and downloaded the album "The 100 Most Essential Pieces of Classical Music"
http://musicbrainz.org/release/b3c2329a-...5bcb406074
So here are the tags that came along with the files. I'll just give the tags of the first track. The principle is the same for the other files though:
Title: Die Zauberflöte (The Magic Flute), K. 620: Overture
Artist: London Philharmonic Orchestra & David Parry
Album: The 99 Most Essential Pieces of Classical Music
Year: 2010
Track: 1/99
Genre: Classical
Comment: Amazon.com Song ID: 214547588
Albumartist: Various artists
CD-number: 1/1
Conductor: David Parry
Copyright: 2010 Telos
So far, so good or bad. However in some tracks the conductor tag is filled with "Johann Sebastian Bach" or "Wolfgang Amadeus Mozart", "Mozart", "Chopin", "Ludwig van Beethoven", "Beethoven". So yeah, quite a mess indeed for a good database.
The composer field is empty for all files.
We have wrong tags, a barrier language (different names for the same piece in different languages, even the ensemble might have different names), typos, a separator "&" in the artist field that kodi can't handle properly, because this could also be just part of the name of a band (Florence & the machine for example).
It would be interesting to see if the files for that album come with other tags from itunes, Google Play and some more sources. I wouldn't be surprised if they come with other tags.
To sum it up, the task to make a valid database out of this mess is quite challenging. I can't imagine how this works without manually re-tagging the files. If kodi develops a guideline how to tag the files in the best way for kodi to handle, I think a lot has been achieved.