Description
As previously discussed in the disc subtitle artwork issue.
I thought about merging this with #697 but I noticed that you'd already assigned it to a release, so I didn't want to delay #697 or pile on the pressure to get this into the same.
Currently only embedded images are considered for disc subtitle artwork, yet there are - at least - a couple of other common approaches in use.
The standard approach is as described by @AverageHoarder in the disc subtitle discussion:
AlbumArtist/Album/CD 1/Disc.jpg
AlbumArtist/Album/CD 2/Disc.jpg
The approach I use, as supported by MinimServer, is to name the image after the value of the discsubtitle tag (%discsubtitle%.jpg).
Should there exist both external and internal artwork I would prioritise the external (similar to how the first embedded image is currently treated) and allow embedded to override at the track level (when in a queue/playlist).
If you'd like some sample data just let me know.