Is this work around still working for you with all the updates? I tried a dist-upgrade after the end of life with the new sources.list when I was trying to install something new and it basically broke the system. I had to do a new install--which on my system means a lot of fooling around to get everything working again.
The avenard repository is still in my sources.list, dist-upgrade pulls in mplayer and libx264-65 from avenard and everything else, including mythtv, from the lmce or ubuntu old-releases repositories. Avenard hasn't updated his intrepid repository in a long time... It just works for me!
Also can you play recorded mythtv files in LMCE and get both video and sound after you do this? I only get video currently with these files and no sound. Many thanks!
Upgrading mplayer will have no effect on playing Mythtv files in LMCE. LMCE will play mythtv files with xine.