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 VLC or Windows Media Player with suitable codecs installed.
We played our 720P MKV movie using the latest version of VLC Media Player and measured the CPU usage with the Performance Monitor built into Windows.
Impressive results in this test, leaving plenty of clock cycles for other applications in the background.