You might have Flash or JavaScript disabled: it's a YouTube video.
Boy am I starting to get tired of companies talking about how much they love HTML5 without walking the walk. Google employes Ian Hickson, the “dictator” at HTML5’s helm,† but fails to support <video> with a Flash fallback. It’s really not hard!
Adobe is guilty of this hypocrisy; Google is quite guilty… only Apple is mostly walking the walk (you never need Flash for any of their web properties), and increasingly Microsoft (no Flash or Silverlight is needed for http://zoom.it).
Edit: YouTube supporting HTML5 ≠ this Google web page supporting HTML5.
And FWIW, even the YouTube HTML5 beta is insufficient — Many times nothing at all will play, even though third-party sites like DetURL or File2HD can find .MP4 files for that video, and the video plays fine on iOS(!). And I’m using Chrome with the plugin completely disabled, for Chrissake — Given there is no technical reason they can’t tell I don’t have Flash, it becomes obvious no one at Google cares about walking the walk.
†Dear downvoters: I am not making up, Hixie refers to himself this way. http://adactio.com/journal/1600/
For me I'm glad it's optional, the versatility of the Flash video player is preferable for me, HTML5 might be fancy schmancy but it sucks right now for features.
edit: also google "why html5 video is not ready"
Apple even uses JS for use cases where one would traditionally use Flash, such as 3D product views, whereas Google still only uses Flash for Street View.
†Do you have an MPEG-4 decoder? I know a lot of Linux distros, and Firefox, only support e.g. Theora out of the box, for patent reasons.
Edit in response to edit: I know all about the various formats, etc. But <video> absolutely is ready, if you’re willing to support exactly 2 formats (MP4 and Ogg Theora) with a Flash-based fallback — something companies offer as an upload-and-paste-simple service.
No it's not. Format is just the tip of the iceberg. It still has many issues such as fullscreen not working/implemented differently, many devices have buggy implementations, it still lacks streaming features that flash does and more. The spec is still lacking.
http://www.google.com/search?client=ubuntu&channel=fs...
or if you're lazy: * http://www.youtube.com/watch?v=_Igz5gdB4uY * http://mashable.com/2010/10/07/w3c-stalls-html5/
Hard to sell people if you're not taking your own stance to heart.
Deploying a site with <video> and Flash is twice as much testing, implementation, and encoding cost as just <video> or just Flash.
Using <video> today (late 2010) is fine for experimental purposes, demos, or for people who are on the bleeding edge. But for mainstream sites who need to reach even people who use IE6, or who don't have much in the way of resources to spend on this kind of stuff, or who simply aren't interested in being the pioneers of new Web technology, then I wouldn't recommend using it yet.
This kind of stuff moves really quite fast, though. Six, twelve months from now? Who knows. Maybe it'll be deployed widely enough and with good enough quality of implementations that using a proprietary plug-in for video will seem positively anachronistic.