What do you mean by not Chromium ? I'm using chromium 4.0.249.64 right now on Archlinux x64 and can watch Youtube videos using html5.
In fact this demo works on my setup : <a href="http://html5demos.com/video-canvas" rel="nofollow">http://html5demos.com/video-canvas</a> so that's theora &#38; h264