Here are some Registry edits to make MCE recognize some of the formats.
[HKEY_CLASSES_ROOT\\.mp4]
"PerceivedType"="video"
"Content Type"="video/mp4"
[HKEY_CLASSES_ROOT\\.m2v]
"PerceivedType"="video"
"Content Type"="video/mpeg"
[HKEY_CLASSES_ROOT\\.mka]
"PerceivedType"="audio"
"Content Type"="audio/x-matroska"
[HKEY_CLASSES_ROOT\\.mkv]
"PerceivedType"="video"
"Content Type"="video/x-matroska"
[HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\Multimedia\\W MPlayer\\Extensions\\.m2v]
"Runtime"=dword:00000007
"Permissions"=dword:0000000f
"UserApprovedOwning"="yes"
[HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\Multimedia\\W MPlayer\\Extensions\\.mka]
"Runtime"=dword:00000007
"Permissions"=dword:0000000f
"UserApprovedOwning"="yes"
[HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\Multimedia\\W MPlayer\\Extensions\\.mkv]
"Runtime"=dword:00000007
"Permissions"=dword:0000000f
"UserApprovedOwning"="yes"
[HKEY_LOCAL_MACHINE\\SOFTWARE\\Microsoft\\Multimedia\\W MPlayer\\Extensions\\.mp4]
"Runtime"=dword:00000007
"Permissions"=dword:0000000f
"UserApprovedOwning"="yes"