As I posted a few weeks ago, the maintainers of the Mythbuntu packages had added the alternative h.264 codec called coreavc as an alternative to the one provided within the MythTV package. After putting some fixes from the ffmpeg project into the core MythTV packages the support for coreavc was removed. If you have a slow system or need the extra 0mph for other stuff or some files still play wrongly coreavc might help you.
The files needed to get a current version of Mythbuntu to build the coreavc packages can be found here.
So, all you need to work this out is to follow the building instructions I gave in this post, but copy the following files into the debian directory:
After building you will have a deb package for coreavc.