VDPAU acceleration for mixing

Hi,

While looking at the VDPAU API, I noticed it already supports mixing
and many postprocessing operations. I would really like to see support
for these accelerations in kdenlive, because it would be possible to edit
HD video without the system stuttering.
I think it will make a great addition to kdenlive, because with the availability
of cheap graphics cards, it is possible to have a good system for editing
HD video, without having to buy a high-end system.
I believe the API also supports off-screen bitmaps, so it could also be used to
speed up rendering.