If you had any remaining doubts about Microsoft's intent to support HTML5 video, prepare to cast those aside. The company has released a third Internet Explorer 9 Platform Preview that puts support for H.264 video via HTML5 front and center.
The screenshot above is from the IMDb Video Panorama demo, in which users can zoom between video thumbnails and click them to play full trailers. The demo also works in Google Chrome, although it's considerably smoother in IE9 thanks to that browser's Windows-specific hardware acceleration.
Other goodies in the new IE9 Platform Preview include support for MP3 and AAC audio, web fonts, some additional CSS3 features, and much more. Microsoft addresses WebM in the release notes, too, saying compatibility with Google's new video format is "not included in this release."