Help identifying music format used in classic Mac OS games
I did some research and reverse-engineering on this recently. The library was called SoundMusicSys, and there's now an open-source version of it called miniBAE (Beatnik Audio Engine) which appears to be mostly based on the original code.

It turns out that csnd resources are just normal snd resources that were LZSS compressed and delta-encoded in a few different ways depending on whether they're mono/stereo or 8/16-bit. cmid resources (compressed MIDI) are just LZSS compressed and not delta-encoded. There also appear to be esnd (encrypted snd) and emid (encrypted MIDI) resources, but I couldn't find any examples of these to reverse-engineer. SoundMusicSys used a few other resource types to link the snd/csnd and MIDIs together; the most relevant of these are SONG and INST, which define the instruments and parameters for each tune.

I wrote a disassembler for classic Mac OS resource forks a while ago, and recently added support for extracting csnd/cmid, INST, and SONG resources in addition to all the normal stuff (snd, MIDI, etc.). Might be useful in playing around with these classic games' content.