This weekend I wrote about Nouveau turning on H.264 video decoding for the pre-fermi "NV50" NVIDIA GPUs. That work was followed by enabling MPEG-4 acceleration for the NV50 Gallium3D driver as well.
It turns out on Friday that NVIDIA's Ben Morris was providing some technical help to Ilia Mirkin while working on this open-source reverse-engineered video acceleration driver code. In a public mailing list post, he provided a few hints regarding H.264 video decoding on NVIDIA hardware, some clarifications regarding internal names, and filling in some previously unknown/magic values for the driver's H.264 structure.
Back in September was when NVIDIA shared they would begin supporting the Nouveau driver and assisting these independent open-source developers with some public documentation. Since then we've seen release a little bit of GPU documentation and then chime in on mailing list conversations from time-to-time as was done on Friday.