Emeric Grange has published a set of nine patches for the Gallium3D G3DVL video decoding stack. These patches largely originate from his work this summer on Gallium3D VP8 video decoding
as part of Google's Summer of Code.
Unfortunately, this patch series isn't introducing VP8 support in mainline Mesa/Gallium3D, but it's other prep work and improvements to the generic GPU video decoding support.
These patches provide better support for some codecs, better documentation, and then the only other patch worth mentioning is MPlayer2 VDPAU support for G3DVL. MPlayer2 is a recent fork of MPlayer
that's gaining a number of features as of late.
Find these Gallium3D video patches from Emeric on the mailing list