Bedroom videos - help wanted

[Rozis]

Yes, i put it more spicy this time...

I'm trying to encrypt .mpg files. I expected the header information at the start of the file. So as a try, i filled the first 60Kb of the file with ascii 0. To my astonisment VLC still correctly played the video!!

So my question is: How does VLC determine a file is a valid mpeg2 video?
Where can i find the header information in a .mpg-file? What part of the file should be encrypted so it can not played anymore withou first decrypting?

As the title say's there could be a use for it....