After seeing the poll results, The most used players are banshee, ryhtmbox and songbird, so I’ve developed the Rhythmbox API so covergloobus can now work with it!
You can download it here:
http://jordihp.deviantart.com/art/CoverGloobus-1-2-118080718
For songbird… the dbus extension is not really complete, and only the artist, song and title can be caught… so there won’t be player controlls neither the album art display so I’ll wait till the extension is more polished!
