MIDIs are currently unsupported, because Apple murdered the One True QuickTime (aka QuickTime 7).
Seriously, go ahead, try to play a MIDI on Crapalina. I'll wait for you...
Back yet? Did it try to load in GarageBand and sound like a dumpster fire?
This sucks in general, but it also breaks the old GameMaker games that used MIDIs.
So I have to figure this out somehow. CoreMIDI on the Mac? Who_Bloody_Knows on Windows?
I had something working using some dylib I forgot the name of on Mac (that also had a DLL), but it might have been GPL which doesn't work. LGPL would work, or public domain or MIT license, etc.