Nope, Window Media 9 is a different codec made by Microsoft team and his mammoth money than MP4. Not sure who made MP4, but WM9 is a totally different codec. Microsoft hired some of the well known scientists to made this codec and quite some money and time too. The results is astonishing, if you ever watch Terminator 2 Extreme Edition, disc 2 contain WM9 playback in High defintion of 1080p with a bitrate of 9.8 Mbits per second or so. Unfortunately, i didn\'t watch the WM9 HD version of it, but i heard you need like a 3 Ghz computer with at least 128 DDR video ram or something to make the movie playback smoothly.