It is not that big of a surprise, but still the most important announcement for the open web this year, Mozilla, Google, Opera, Adobe, and many other companies have announced WebM, a new open media project that aims to develop an open alternative for creating video and audio content for the web.
WebM uses VP8, the efficient video encoding format Google got when it acquired On2 Technologies (a process completed earlier this year) and is now relicensed under an open BSD license, Vorbis for audio encoding, and a subset of popular Matroska as the video and audio container.
More surprisingly, all browser vendors already have development versions that support the new WebM. You can get Opera, Firefox, and Chromium builds right now.
ffmpeg, DirectShow, and the VP8 SDK are the current options for encoding and creating WebM-enabled applications right now, with even a few commercial alternatives already available as mentioned in the WebM Tools section. The specification is labeled as final, so developers can conifdently start hacking according to the site.
As for content, there are already 1.2 million YouTube videos available in WebM. The WebM site provides instructions for watching WebM video which involve URL tweaking. Google has also announced they will transcode all YouTube videos to WebM.