What is DxVA?

What is DxVA?  
DVD or HDTV uses video compression technique called MPEG2.
It requires lots of computing power to decode MPEG2 streams to uncompressed video.
Even current fastest CPU does not have enough power to decode full resolution HDTV.
Graphics chips manufacturers integrated some function of the MPEG2 decoding algorithm in their graphics chip to aid decoding of the MPEG2 streams.
But it was proprietary architecture and it was hard to use the function for the developers of outside of the chip company.
So Microsoft Corp. made a common API that MPEG2 decoding programs can make use of the Graphics chips capability of MPEG2 decoding regardless of the graphics chips used. This driver is called DxVA(DirectX Video Acceleration).
Unfortunately not all graphics chips and/or driver combination support DxVA.
At the time of this writing ATI Radeon series and drivers are the graphics chips that support DxVA well.
Using DxVA full resolution (1920x1080) HDTV stream can be decoded 30fps/sec using less than 50% of CPU on P4 1.8GHz.

Graphics : ATI Raden7000, 7200,7500 with DDR video memory or
        ATI Radeon 8500,9000,9500,9700,9800
        nVidia MX420, 440, FX series

DXVA Support: the good news here is that ATI was heavily involved with Microsoft when it formed the DXVA standards for MPEG2 acceleration. The original Radeon supported the full feature set of what would become DxVA even before the standard was finalized. On the NVIDIA side, NVIDIA added a new video processor to their GeForce 4 MX series that is fully DXVA compliant. The GeForce 4 Ti was focoused on 3D gaming and so the silicon went to 3D piplines rather than the video processor the GF4MX had. By the GeForce FX series technology has progressed enough for NVIDIA to put the GeForce 4 MX's video processor into every one of the FX line.