I have several MIDI files on my computer. They ALL play fine on 10.10 or earlier, but in 11.04 Natty maybe only about 50% of them play. Totem will recognize all the files in Natty and even show track time and show the song playing, but no audio. Anyone care to venture why some MIDI files work and some dont in Natty? The same files work fine on 10.10 and a 10.04 system.
I have the same problem.
The best workaround I have found (to save downgrading) is to just install Timidity++ and then associate one of the interfaces (I use the GTK+ one) with MIDI files. It is not the best solution for instance if you have any midi files in your Totem playlists you will still get silence, and also means that you have to have two music players, but it lets me play all my MIDI files.
I'll post back if I find a better solution.