Google’s new HTML5 YouTube player has received a number of major updates recently to improve its features and performance, and is now coming on par with YouTube’s Flash based player .
Recent updates to YouTube’s HTML 5 player have added support for closed captioning and annotations, together with native fullscreen support for Firefox users, amongst others.
YouTube has been offering YouTube users the option to use the new HTML5 player for over a year, and allows you to opt for the HTML 5 YouTube player over the older Flash based one.
You can signup to the ongoing trial to use the new HTML5 YouTube player here, if you would prefer. Unfortunately, though when ever any YouTube movie has an advertisement in it YouTUbe will still force you to use its Flash based player for the time being, even if you are a member of the HTML5 trial.
Source: TNW : Google Blog