Implement the 'Album Artist' ID3-tag as a TXXX-tag

[Albin Jacobsson]

Implement reading and writing to the unofficial ID3-tag 'ALBUM ARTIST' using the TXXX-marker from the id3v2.4.0-frames standard.

[Johannes Sasongko (sjohannes)]

The problem is that some players use TXXX:Album Artist, while others
use TXXX:AlbumArtist or TPE2 (Band). And then there are others using
their own label (Quod Libet uses TXXX:QuodLibet::AlbumArtist).

And isn't this a duplicate?

[reacocard (reacocard)]

Johannes - Not a strict dup, its a more specific request and imo worth leaving on its own.

As far as TPE2 goes, I think reading that directly as albumartist is not ideal as some people may actually use it for its intended purpose. We can add an option or tools in the tagger or something for people who do need TPE2 albumartist. For those in the TXXX namespace, I don't see why we can't support all the common ones at least. Just have a preferred ordering of TXXX names and use the first one that exists in the file when reading/writing, or the first in the list if it doesn't already have one. Will probably require some hackage of the xl.metadata system since its currently designed for static one-to-one mappings, but shouldn't be hard to implement.

[Johannes Sasongko (sjohannes)]

> Johannes - Not a strict dup, its a more specific request and imo worth
> leaving on its own.

Hm. I remember discussing this feature somewhere, but I can't find a
bug report for it. Maybe it was in the forum.

> As far as TPE2 goes, I think reading that directly as albumartist is not
> ideal as some people may actually use it for its intended purpose.  We
> can add an option or tools in the tagger or something for people who do
> need TPE2 albumartist.

Going by your planned scheme (of having a priority list) I guess we
could add this as another entry when the option is enabled.

Meh, I find it ironic that the blatantly non-standard tag is actually
the closest we have to a standard.