I also have the same thing (sketch/png media type complaint), and my app manager doesn't work - Faster App Manager does, but the regular one won't start up.

I keep needing to reinstall some other stuff to get the decoders-support working after every reboot - just restarting the trackerd/indexer don't help. kmplayer will play things fine but the built-in player won't play anything ("Operation unsupported" yellow error banner when I try to press pause and no result on any other button, just sits on the "currently playing" screen at 0:00)

Some other dbus stuff seems to be missing/not working properly.