Play mkv files
This page explains how to achieve successful playback of Mkv/H264/X264 files on Linuxmce 810 with some limitations.
The following instructions will allo playback of most types of mkv containers with VDPAU, but the instructions will break VDR.
You will have to forcefully install a backported libxine prepared by niz23. The debs they are located here: http://tschak.homelinux.com/deb/ They need to be installed all at the same time, with dpkg. Note that there is no support for these packages, and they WILL break VDR.
Troubleshoting
Another method, if you see green artifacts, is to rename the files to .m2ts and changing media type to "LinuxMCE Blu-Ray". This makes LinuxMCE use mplayer to play mkv files instead of xine, however in that case you loose the ability to pause.