How to detect whether an HTML page contains a video?

I would like to know whether it a possible to detect whether a HTML page contains a video.

I know that one possible way is to look for ".swf" in the HTML source code. But most of the pages do not contain the file name.

For example, given following URL and possibly its source code, is it possible to find out whether it contains a video: http://www.cnn.com/video/