Gputrans
From MythTV Official Wiki
gputrans is a project by Gavin Hurlbut to attempt to put some to all of the calculations during transcoding into the GPU of the nVidia Geforce cards (and later ATI Radeon).
It currently is in the planning stages, and donations will be gratefully accepted to spur it on. Donations can be made at http://mythtv.beirdo.ca/gputrans/donations.php and will be used solely for the furthering of this project.
For further details, go to http://mythtv.beirdo.ca