HTML 5 Video player on youtube has been launched some time back, in order start using this player you will need to join the html 5 beta program, go to this link
to join this program and enable this player for the video you watch. This is an opt-in experiment for HTML5 support on YouTube. If you are using a supported browser, you can choose to use the HTML5 player instead of the Flash player for most videos.
Following is the list of all supported browsers
Following are some other important things that you should know before you view a video in HTML 5 player.
Why View a Video On HTML 5 Player ?
- Fullscreen support is partially implemented. Pressing the fullscreen button will expand the player to fill your browser. If your browser supports a fullscreen option, you can then use that to truly fill the screen
- The HTML5 player has a badge in the control bar. If you don’t see the "HTML5" icon in the control bar, you’ve been directed to the Flash player (due to restrictions listed below)
- The HTML5 player also has a badge to indicate the video is using the WebM format. If you don’t see the "WebM" icon, the video is encoded using h.264
- If you want to find videos with WebM formats available, you can use the Advanced Search options to look for them (or just add &webm=1 to any search URL)
Because it is much better and faster than default flash player, another good thing it that it does not require flash support or any flash supporting plugin to play the video in your browser.
How To View Video In HTML 5 Player
YouTube has a special parameter that lets you do that: just append "&html5=True" to the video’s address.
Here’s an example given below
[ Via Google Operating System