http://apple.slashdot.org/story/10/04/30/1037230/Microsoft-Tips-the-Scale-In-Favor-of-HTML-5
Microsoft Tips the Scale In Favor of HTML 5
"Dean Hachamovitch, General Manager for Internet Explorer at Microsoft, has announced that IE9 will use only the H.264 standard to play HTML 5 video. Microsoft seems to have become very committed to HTML 5, while Flash loses even more ground. The announcement came the same day Steve Jobs detailed why Apple does not accept Flash on iPhone and iPad."
http://blogs.msdn.com/ie/archive/2010/04/29/html5-video.aspx
IE9 will support playback of H.264 video only.