m64 format documentation

[Sauraen]

Through reverse-engineering of the SM64 audio library, I figured some more details of the m64 format.

The hack64 forum software doesn't seem to support tables, but here's an external markdown doc: https://hackmd.io/opEB-OmxRa26P8h8pA-x7w as well as a decoder: https://gist.github.com/simonlindholm/30...22c291f878

The list of commands should be complete, though some of the descriptions are a bit vague. I could look closer into the code if there's some particular aspect that people are interested in.

Awesome work simonlindholm! How did you figure the rest of the commands out? Just by reading the disassembly? There are a lot of data structures used by the sequence parsing, and even with stepping through the code in an emulator it is very difficult to figure out what all the fields would be.

I'm the author of SEQ64, which is software for importing/exporting this sequence file format from/to MIDI, both in SM64 and the other first-party Nintendo games which use versions of the same file format (most notably OoT and MM). SEQ64 is also the backend for N64 Sound Tools for the games using these formats. I figured out many of these commands years ago, starting from previous work by Deathbasket, when I was developing the program, but I was never able to figure out the rest of them. I hope you were able to build on my work--I see you're using my notation of "Q" for the accumulator, so I'm hoping you were able to start from the sequence definition in SEQ64 and figure out the rest from there.

The reason SEQ64 is 20,000 lines of code rather than a few hundred is because it allows the definition of the sequence format to be specified by the user, rather than being hard-coded into the program. This was primarily intended to avoid minor differences between games causing the program to only be usable for certain games or versions, because nobody wants to change the code and recompile it. But that does mean it became large and unwieldy in some ways, and it was never able to use the scripting capabilities of the format besides optimizing data with calls and loops. It would be nice to have a full script editor that's complementary to SEQ64, where you could import a MIDI with SEQ64 and then edit it as a script with the other tool. Of course, this tool should also work on OoT and all other games using similar formats, which is a lot to ask!