The patch published ahead of the weekend is quite straightforward and builds upon the work by Ilia over the summer when he already enabled MPEG-2 and VC-1 video acceleration for NVIDIA GPUs with the VP3/VP4 engines. This change affects the GeForce 9300 series hardware as well as the GeForce 200/300 series GPUs and allows for H.264 content to be decoded using the Gallium3D VDPAU state tracker with this open-source NVIDIA driver.
Still to be tackled is seeing whether MPEG-4 acceleration will also work for NVA3+ (pre-Fermi) GPUs. The patch to enable H.264 for the VP3/VP4-based GPUs can be found on the Nouveau mailing list and could end up in mainline Mesa Git soon for the next release. The patch has also been proposed for backporting to stable Mesa releases.