A while back, YouTube released a demo of a video player based on HTML5. The demo was popular, and since then, the company posted a blog regarding a "pre-spring cleaning effort," which led users to let YouTube know that they wanted more content based on the update to the markup language. Google's given that the thumbs up, and announced today that an experimental version of an HTML5-supported video player is available.
The announcement blog post (found here) revealed the changes, though at the same time, the limitations were also listed; the HTML5 player doesn't support videos that have advertisements, annotations or captions, and it's obviously only compatible with browsers that support the new web standard as well as h.264 encoded video. That means that if you're using Chrome, Safari, or Internet Explorer with Google's ChromeFrame, you're in luck; anything else, too bad. While this sounds restricting, you have to keep in mind that it's still relatively new technology and that companies catch up pretty quickly when they need to.
If you'd like to try a video that uses the new HTML5 video tag, visit YouTube's demo page. Be warned though, as YouTube stated that this will enable HTML5 video for your browser, provided that you meet all the aforementioned criteria. Additionally, if you've enabled other experimental projects with YouTube, you may not get the HTML5 player working correctly. You can manage your enabled or disabled experiments over at TestTube, should you need to. Let us know how it goes!