The gstreamer-vaapi package provides a collection of plug-ins so that this media framework can take advantage of this video acceleration API that's exposed either directly or via one of Splitted's back-ends to most Linux graphics hardware. These plug-ins are fully open-source and support MPEG-2, MPEG-4, H.264, VC-1, and WMV formats. This Splitted Desktop Systems code also supports OpenGL rendering through VA/GLX or GLX texture-from-pixmap + FBO.
The release announcement that contains all of the details concerning these open-source VA-API plug-ins for GStreamer can be found on their development list.
Two months ago there was the release of a new Fluendo Codec Pack that provides legal plug-ins for GStreamer at a cost with VA-API and VDPAU support, but now there is this open-source alternative thanks to Splitted Desktop Systems.