WOW!! That was an incredible amount of work.
On the YouTube page, the guy said "This was the most challenging project I have ever undertaken, consisting of 3D tracking, seamless camera cuts and 3D camera projection."
Here's a follow-up video talking about the portal gun which is actually a 3D model and not a real gun of any kind.
Portal is a very popular game to create movies from. Partly because the guys who made the game used very high polycount models so that part is done for you. There's another one too.