VDPAU (Video Decode and Presentation API for Unix) is an API developed by NVIDIA which offloads the processing of various video codecs onto the GPUs of certain models of NVIDIA video cards. This brings the features of PureVideo, currently available in the Windows drivers, to the Linux platform. Offloading the processing of video to the GPU can drastically lower CPU utilization, and allow lower-end frontends to still process highly intensive video codecs like h.264.
VDPAU was announced to the mythtv dev list on Nov 15, by Andy Ritger, Manager of the NVIDIA Linux driver. Within 4 days, Issac had posted a POC (proof of concept) patch to the mailing list for VDPAU support within trunk, saying "Preliminarily, this stuff looks _very_ promising." On November 29, Changeset 19165 included preliminary support within trunk. While the VDPAU support is still in it's infancy, in both the driver and myth, several testers have responded saying that they are able to use VDPAU with limited issues. Running current trunk for VDPAU support is currently not recommended except for testing and bug reporting purposes only.
OSD - TODO: explain where and what is affected
Tearing - TODO: explain where and what is affected
Interlacing - TODO: explain where and what is affected