New YouTube videos are now saved in WebM format.

All new videos uploaded to YouTube are now transcoded into WebM format in addition to other supported formats.

WebM is an open video format designed to replace the H.264 proprietary video standard. Its development is sponsored by Google and its use does not require license fees. Chrome and Opera support WebM, the format has been added to Firefox last month, and a plug-in has been announced for Internet Explorer that will add it.
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In addition to transcoding all the new videos in WebM, the YouTube team is working to transcode all the videos into WebM. However, given the amount of content on YouTube (allegedly daily users upload videos of a total duration of six years), this is quite a challenge. Nevertheless, it was already possible to transcode video, which views account for 99% of all views, or 30% of the entire video.

YouTube is said to continue to support the H.264 format. Also, developers will continue to develop HTML5-video player, announced last year.