The improvement is possible thanks to a new feature called Stage Video, an API that delivers high performance video playback across platforms and which can shift most of the work for Flash video to the GPU. It leverages complete hardware acceleration: not only does the GPU offload H.264 hardware decoding (introduced in Flash Player 10.1), but it also handles the rest of the video rendering pipeline, including color conversion, scaling, and blitting. Stage Video requires Flash developers to update the code in video players, so simply updating to the new player won't automatically improve CPU usage on all sites, although YouTube has already updated its player and others will likely follow.
"In addition to decoding the data, [Flash] has to convert YUV data to the RGB colorspace and combine the image with other Flash elements," Adobe Engineer Mike Melanson said in a statement. "Then it has to cooperate with another application (web browser) to present the video to the user… It plays linear media files from start to finish while combining the video with a wide array of graphical and interactive elements (buttons, bitmaps, vector graphics, filters), as well as providing network, webcam, and microphone facilities, all programmable via a full-featured scripting language."