I've been using this on 3.x for a long time. Now I switched to 5.x and I thought more people might be interested, so I recompiled and submitted.
It depends on many other extensions, didn't figure out a way to avoid this in an easy way, sorry.
But I think it should make HD video usable on platforms like thinkpad x200 that I'm using.
You can probably figure out if your system is supported from the readme in i965-va-driver-g45-h264_1.0.19-1. From this it looks like h.264 is not supported for CTG, but actually it works on my Intel GMA 4500MHD.
libva-intel-driver is the VA-API implementation for Intel G45 chipsets
and Intel HD Graphics for Intel Core processor family.
Platform definitions:
CTG: Cantiga, Intel GMA 4500MHD (GM45)
ILK: Ironlake, Intel HD Graphics for 2010 Intel Core processor family
SNB: Sandybridge, Intel HD Graphics for 2011 Intel Core processor family
IVB: Ivybridge
Codecs
------
H.264 D ILK+
H.264 E SNB+
MPEG-2 D CTG+
VC-1 D SNB+