One of the 2013 X.Org GSoC projects is adding X-Video support to GLAMOR. GLAMOR is the 2D acceleration library required by the AMD Radeon HD 7000 series GPUs with the RadeonSI driver stack while it can optionally be used for older Radeon GPUs or Intel hardware too.
The plans for this X-Video GLAMOR support are laid out in this blog post by Chuan He, the student working on this code and being mentored by Nouveau's Arthur Huillet and AMD's Alex Deucher.
The plan for this X-Video support comes down to stubbing out X-Video for GLAMOR and then writing OpenGL and GLSL shaders for doing YUV conversions and other color adjustments for video playback. This would be a generic way of improving the video playback process a bit, but still not obviously as good as tapping AMD's UVD or NVIDIA's PureVideo engines for full video encode/decode acceleration over VDPAU.
At the end of June, Chuan He shared a status update for X-Video GLAMOR support (only now is it coming across the FreeDesktop.org Planet), but there isn't too much to share. In a post last week the student developer was hitting corruption within a GLAMOR dispatch function and presently debugging the issue.