I've also added a MUS lump (music format used by DOOM) player, using the MIDI message functions in winmm. The only feature left unsupported is the pitch wheel, as I can't quite work out the MIDI command for it.

If somebody could please explain the logic behind MUS, please tell me. It's essentially the same as MIDI, except each command has a different byte (so you have to convert to the correct byte first), uses channel 15 for percussion (so you have to swap 15 with 9 and 9 with 15 - as 9 is the MIDI percussion channel) and uses a controller for a patch change, whereas MIDI has a specific patch change command rather than lumping it with the controllers.