Well, that means that it's playing the half presses for the shoulder triggers correctly. Not sure why it's not working for movies you make. (Also, are you sure you didn't see the crosshair? It's supposed to show up if R is pushed in all the way, which I do when looking down, but not up. It should look like
this.)
The header for .dtm files are detailed
here in the DTMHeader structure, but not all the fields are used or even set yet. (gameID is ignored for playback at the moment, uniqueID isn't set, and all the fields after numRerecords are not set yet.) The format for the Gamecube controller is the ControllerState structure. I'm not sure how Wiimotes are stored. I think we just store the raw emulated USB packets for it.
EDIT: The comment for numControllers is outdated. It now is a bitmask of the controllers used. (First 4 are GC controllers 1 to 4, last 4 are Wiimotes 1 to 4.)