Overview
The main motivation for VA API is to enable hardware accelerated video decode at various entry-points (VLD, IDCT, Motion Compensation, deblocking) for the prevailing coding standards today (MPEG-2, MPEG-4 ASP/H.263, MPEG-4 AVC/H.264, and VC-1/WMV3). Extending XvMC was considered, but due to its original design for MPEG-2 MotionComp only, it made more sense to design an interface from scratch that can fully expose the video decode capabilities in today's GPUs.
Read more about this topic: Video Acceleration API