YouTube launched an experimental version of the site that used the built-in multimedia capabilities of web browsers supporting the HTML5 standard

In January 2010, YouTube launched an experimental version of the site that used the built-in multimedia capabilities of web browsers supporting the HTML5 standard. This allowed videos to be viewed without requiring Adobe Flash Player or any other plug-in to be installed. The YouTube site had a page that allowed supported browsers to opt into the HTML5 trial. Only browsers that supported HTML5 Video using the MP4 (with H.264 video) or WebM (with VP8 video) formats could play the videos, and not all videos on the site were available.