The idea something for showoff, not for functionality. Not something for composing work. Your improvisation will lose wings with that. About tracking motions coming from a camera, this is not a very good idea, camera resolutions that one could afford are far-far too low to have any descent control over anything, an alternative would be infrared tracking that is not too expensive, principally you can buy a headtracker or P5 glove and take it to parts and adjust it to your needs. As I see, most of the input controllers available today are crap, as they operate in very limited time-space dimentions. That goes for speed calculated touch sensitivity, piezo solutions that you must hit with a stick and hit them strong, even most expensive hand percussion controllers are relatively dissapointing. I've been looking for best input controller for about 10 years now and closest match to human hands are in my opinion, zendrum, kat percussion controllers and some custom Force Sensitive Resistor based keyboards that I've tried. Combining these with breath control you could have nearly satisfiying results in terms of sensitivity. I see it as a challenge of evolution, human hands and voice have bit more history than input controllers available today, but the speed progress and directions where things are going, are promising. My thumbs go up on this one because it makes people think about controlling forces to express them in different ways than they are used to and experiment with them. If I could make the difference in my youth, I'd study a bit more math and physics and smoke a bit less weed so I would be smart enough to today to build an input controller that would be a table covered with touch pads for location, under these force sensitive resistors. Additonal controls would come from infrared head tracker and breath control. Some P5 gloves broken to pieces and made to track other motions would be also useful. It sounds like something for virtual reality, but hey, define music.