For anyone else confused: Press play before you try clicking the time markers.
Looks pretty useful apart from that!
Design could use some more work, but I like the idea. Consider using social plugins for users. Also I love how you chose to show it off with YC's lecture. I guess you had to wait a while for the video to be online but it was probably worth it. That's thinking out of the box.
Thanks! We initially made the site for a competition at school but then took it down after we decided we didn't want to continue working on it. We decided to revisit the project a couple days before the YC class and put up the new YC lecture. The design definitely needs some work and there are a lot of crucial features missing, but we'll be adding more stuff soon.