The Matroska Media container is a very popular, open standard Multimedia container which is usually found as .MKV files. It is a very popular format in enthusiast circles and can be played directly in Windows Media Player with suitable codecs installed. We use the Combined Community Codec Pack (CCCP).
We ripped our BluRay disc of Batman: Dark Knight to 1080P MKV and used Windows Media Player to play back the file.
No problems coping with this test, with plenty of CPU cycles left over for multitasking.