Or if I were to continue this as primarily a Flash project (I had imagined doing the main thing as an EXE so that you could get to a song library locally, and this just being a quick demonstration) I could allow uploading songs and pre-analyze them with something else on the server side, and then use the game to read the song and generated data file without having to process it whenever a song is played...

Though this is rapidly becoming something I should push off until existing projects are finished!