Don't see how that's possible without the OS exposing some kind of API, or if the browser latches on to that API. Either way, there is no portability here. Your best bet is Java, not JavaScript, or maybe just plain ol' Flash.
I'm sure it would be relatively trivial to make an activex plugin to support <video> and <audio>. The trick is getting the IE drones to actually install it... most of them are still using IE6, which is now 2 versions behind as of a few weeks ago.