Cool stuff. Reminds me a bit of how http://soundcloud.com does a similar thing with music. Check it out if you haven't, yet. It's a really well done solution IMHO.
Thanks! I agree, Soundcloud does have a pretty slick implementation. I've definitely tried to learn from their design. Viddler also has a similar feature, and more related to online video. I think what popcorn.js and these other tools are trying to do is pretty exciting. There's still lots of room for improvement.
