Audio in HTML5 is a nightmare (see our blog posts on the subject). Different browsers support different formats, and different formats require different encoders, and some encoders are expensive and would mean putting up the price of C2.
We managed to get audio working after significant effort and some hacks to get around encoder licensing (e.g. using Windows 7 itself to encode AAC). However, the situation for video is even worse. Getting it to work at all would be a long and difficult project, and we don't really have the resources to spend doing that right now. Not only that but videos are also often extremely large and incredibly bandwidth consuming which makes them unsuitable for lightweight casual games. So I'm afraid given all this we aren't really planning on adding video support for the forseeable future.
It's possible somebody could write a plugin that supports this. However, you would have to deal with the difficulties of encoding to multiple video formats yourself.