Nouveau VP2 H.264/MPEG2 Decoding Now In Gallium3D
Phoronix: Nouveau VP2 H.264/MPEG2 Decoding Now In Gallium3D
While Radeon DPM for Linux 3.11 is most of what Linux enthusiasts are talking about, the Nouveau changes in Linux 3.11 include support for H.264 and MPEG2 video decoding. The necessary user-space driver changes have now been made for supporting this accelerated video decode process from Nouveau Gallium3D...
The NVIDIA chips that feature VP2 are: G84, G86, G92, G94, G96, GT200 - you can see in lspci if your card is one of those.
They are usually called NV84, NV86, NV92, NV94, NV96, NVA0 at nouveau, the names mentioned above are how NVIDIA calls these chips, and how they're shown in lspci.
Nouveau in Ubuntu 13.04 shets the bed. Could be Compiz related.