After a long interim period I now know that the proposal has been accepted. Rather than sit around I've been working on getting things up and running, so I'm glad I got a head start on things. It took a lot of digging through Mesa code and some questions to the dri-devel mailing list and IRC channel, but I've managed to get some basic initialization out of the way. I've also implemented enough functionality and stubs to get some basic test cases compiling and running successfully. I found a port of mpeg2play on Mark Vojkovich's web site that uses XvMC and have managed to get that compiling and running. By running I mean not crashing, it doesn't display anything as of yet, but at least I'm heading in the right direction.
Now I'll need to figure out how to get XvMC surfaces onto X drawables with Gallium3D. For some reason most of the XvMC functions don't take the XvMCContext as an argument, so I have to store that along with each surface, and yet they all take a pointer to Display, which I don't see a use for. A headache more than anything else, but it seems counter-intuitive to me. Also, the Gallium3D API is new to me and it will take some time to figure out. Keith Whitwell provided me with an in depth explanation of how to start on the state tracker and winsys thankfully. I'm hoping by the end of this weekend I'll have something on screen, even if it's garbage (i.e. the video frames before IDCT). I'm also hoping to get started on writing shader code to do the color conversion. Stephane Marchesin, my mentor for this project was kind enough to point me to the current Xv implementation for the Nouveau driver, which does color conversion and bicubic interpolation in shaders currently.