Prefer embed album art to folder album art

[NyaomiDEV]

AKA: If the track does have an album art, grab that instead of the folder album art.

This is because there may be random images in the tracks' folder, such as booklet scans.
Also, this would fix a current issue where some singles don't have any art displayed even if they have their own embedded in their tags. That's because some media players create an "AlbumArt.jpg" / "Folder.jpg" on folders full of singles; then Mopidy-Local scans the folder and doesn't know what to do precisely (and I personally noticed this behaviour, I don't even know if it's somewhat intended at this point).
This issue could be worked around by creating a subfolder per file, but that process is tedious and problematic for huge music collections.

[orontee]

I faced that problem with a music library managed with MusicBrainz Picard application. But playing with the application parameters, the image for the front cover can be named cover.jpg even when there's other images for the booklet, etc. Then customizing mopidy-local album_art_files one can have the front cover image to be used.

[fkuersch]

I have a bunch of unrelated MP3 files with embedded images. mopidy-local doesn't extract the image of the single track. But if I set the 'artist' and 'album' metadata, mopidy-local does find and extract the image.

Unfortunately, this method also spams the "My Albums" section in mopidy-iris by creating an album for each individual file.

[jotak]

Maybe the approach for providing art should be changed more deeply: instead of having a list of images per album (which is per design in the database), it should more stick to the actual model with 1 or 0 image per track, and 1 or 0 image per album.

That would of course break the Mopidy-Local API, so it is then up to the frontends to display the correct image depending on the situation. But I think it would solve many problems (including what @fkuersch mentions about albums view bloated with different images)