Adobe just released the public beta of Flash Player 10.2 which (among a few other cools things) adds cross-platform GPU based video rendering which increases video playback performance.

To compile SWFs that take advantage of the new feature you need the new Flex 4.5 "Hero" stable Build 4.5.0.18623 which was also released.

More information and a lot of sample can be found here and here.

Dirk.