I know that some sites have a sort of encrypter on their videos. When you load the video, the real url of the video is encrypted so it can't be stolen/downloaded. How can you do this? Is it some kind of php script?
I would guess so. You could do it in php for sure. Just make an algorithm in php and your done. I did a similar program for VB.net, although it had to be more complex because people can take apart your code or crack it fairly easy. Good luck! (You might try creating your own alphabet where a lower cased A would equal "a1" and an upper case A would equal "A1" all the way to z.)
I've seen people use php and .htaccess to make virtual directories. The .htaccess shows a different directory for the video than where the file actually exists. Also, you can limit any direct access to files in a certain directory. It would make it much harder to steal content from that directory.