So how do they get it to show in Windows Media Player? Make a fake one that is the exact same as my colourized version?
It's almost always a little GIF or short animation, that links directly to the "codec" after showing an alert.
If WMP actually loads a video and asks for a codec, then it's a legit video.
Personally, I have yet to encounter any video that I don't have a codec for. K-Lite is pretty thorough.