ARS Technica measured the CPU usage during HD video playback on ATI and NVIDIA based graphics cards:
Video card gaming performance traditionally gets most of the coverage whenever ATI and NVIDIA go head-to-head with new products, and it makes a certain amount of sense given that gaming is a traditional driver of discrete graphics card sales. But gaming isn't the only field on which ATI and NVIDIA compete. Today I'll be examining high definition video image quality and CPU usage during HD decoding on a set of current ATI and NVIDIA cards.
Check it out over here. Overall ATI wins in VC-1 and H.264 decoding but NVIDIA wins in 1080i decoding.