This is a massive step in the right direction. I remember some time back when the On2 codec was introduced people were asking about H.264 and it the responsed was that is was too CPU intensive, which I guess now must have been resolved.
You will soon (with the release of Flash Player 9 Update 3 Beta 2 be able load and play .mp4,.m4v,.m4a,.mov and .3gp without any chances to your code.
Adobe official announcement here and there’s also some invaluable info going into the details of the implementation over at Tinics blog here.
The update als0 includes:
1. Enhancements to full-screen mode to use hardware scaling for improved video performance and quality on systems running Windows 2000 and newer or Mac OS X 10.2 and newer.
2. Faster rendering of vector graphics on multi-core CPUs.
3. Higher quality and performance for downscaling large bitmaps (SWF 9 only).
4. Support for caching common platform components, such as the Flex framework, to reduce average application sizes. This feature is enabled in the Flex 3 beta available on Adobe Labs.
5. Support for full-screen mode on Linux.
Wanna test it out? Well you can as the player is available on labs here.