The video codec to be used in HTML5 has had quite a lot of debate. Apple and Microsoft have been backing H.264 whereas Mozilla wanted Ogg Theora. Today, Google has introduced WebM that is based on the VP8 technology Google got with their acquisition of On2 Technologies.
In a rather swift blog post within hours of WebM being announced, Dean Hachamovitch (General Manager, Internet Explorer) said:
In its HTML5 support, IE9 will support playback of H.264 video as well as VP8 video when the user has installed a VP8 codec on Windows.
All eyes are on Apple now. With Opera, Firefox, Opera and Internet Explorer backing VP8, video on Internet seems to have some consensus. Even Adobe, at Google I/O said that they will be adding VP8 support for Flash. Technically WebM is a container, which uses VP8 video and Ogg Vorbis for audio.