I'm all kinds of picky, so when I wanted to start demoing how to trigger events with sound like they do in games like Guitar Hero, sound alone just wasn't going to cut it. So I started playing with the idea of integrating MIDI into Sound Reactor. Six months later (the 1 year anniversary of Sound Reactor - give or take a few days) I released the Pro version of Sound Reactor.
The MIDI portion was written from the ground up just for Sound Reactor Pro. There's LOTS of documentation out there on the subject, so a BIG thanks to everyone who has documented the file format.
The end result is that Sound Reactor Pro generates a spectrum from MIDI note events played back from a type 0 or 1 MIDI file. Since Sound Reactor reacts to frequencies in a spectrum, this was a very natural upgrade.
Since MIDI stores more than just note events, I knew I needed to make it possible to handle the events manually. You can attach your very own MIDI event handler and process the events however you please.