WMP embed is not working in MP4 and WEBM

I'm modifying a legacy application (which if or if it needs to work in IE6 with Windows XP on my VM, I'm not crazy). WMV, MPEG videos are played, but MP4 does not play in the browser. Even if I have the latest compatible version of K-lite installed with XP.

I have tried WMP9 and WMP11 but neither of them worked for me.

I am pretty sure the embedded control has lots of limitations when used inside a browser due to security reasons. It probably only loads the standard codecs from Windows. Which on XP means it can pretty much only play WMV and MPEG1, and a few old video formats in AVI.