As reported by Podcasting News here, Wikipedia is using .ogg Theora video rather than H.264. It looks like there is a Java applet player that works sometimes on Mac Safari 4 and is out of sync. It plays on Mac Firefox 3.6 and sometimes on Mac Chrome 5 and is out of sync. Of course these things are subject to change but that's how it is today. The battle for open vs. licensed continues. As Gruber points out here, ogg video will probably never play on a mobile device since there is no chip level decoder support for ogg as there is for H.264 and it will be a big battery drain since it will need to use the CPU. I agree him that most sites will use H.264 since with one encoding they can play in both the HTML 5 <video> tag (on most browsers) as well as Flash players for the browsers like Firefox that don't directly support H.264.