Milo files can contain so many things, everything from 3D meshes to character animations. It’s basically Harmonix’s proprietary archiving format. If you look through their game files, you can see how the format has evolved over the years. The extension has changed too. There’s .rnd, .rnd.gz, .rnd_ps2, .gh, .milo_ps2, .milo_xbox, etc. But they all follow the same basic structure, they have a header the lists all file names with their corresponding type in the archive and they’re usually compressed with either Zlib or Gzip.

Amplitude was the first HMX game to start compressing that data into blocks. Up until Guitar Hero II on the PS2, the header data was easy to parse as it only listed the files in the archive but GH2 added things like imported milo file paths, embedded DTB files, and what appear to be view matrices data. And it doesn’t help that the header structure appears to dynamically change depending on certain values that I have yet to pinpoint. To add to that mess, now milo files can contain additional milo files embedded into them.

But does the Milo file also have drum animations, left hand animation and the camera stuff? also I think I know how to do good lip sync now anyway.

For custom songs, the milo files only contain lipsync data up to three parts. HMX authored songs can contain up to four lipsync parts as well as additional data such as camera cuts and the text events for each instrument track, such as “play” and “idle” cues.