It is worth pointing out that Chrome and IE are miles ahead of Firefox and Safari at time stretching audio. Firefox and Safari sound like an underwater mess. Chrome and IE use a sophisticated and very nice pitch correction algo (I think it is called WSOLA)
Yeah, the whole advantage to HTML5 video is that it's just a video in a standard format. Your client (browser, whatever) can do whatever it likes with the video. Usually the UIs just present pausing, rewinding, maybe time-stretching. But in theory it's just a video and you can do any kind of analysis and editing on it you want.
