I notice that unless I specify (for each album) a picture manually, cover art is not passed to the ubuntu music menu (or any of the gnome-shell multimedia equivalents for that matter). Once a photo has been selected, usually by right clicking on the album and setting a photo that *points to a jpg*, it works.
It does NOT work if the image is embedded in the music file. The behavior seems consistent across differing music types (m4a, mp3, etc). Covert art detection within gmusicbrowser itself works fine, I only see this behavior with the sound menu. This has been a problem for as long as I can remember, it's only today I got fed up with it and decided to file a basic bug report. This happens on two seperate machines, both with the stock gmusicbrowser provided by ubuntu and the shimmer ppa version.
I imagine this is a bug in the mpris/mpris2 plugins. I have both enabled. If more information/config dumps/whatever is needed I can provide them, but I figured this would be a good place to start out.
thanks for pointing it out, it's indeed a known problem (and has been since the creation of the mpris2 plugin). it seems to be a problem with the implementation of mpris2 in ubuntu's soundmenu.
i'll check again with upstream (gmusicbrowser) and try to keep this updated.