Quick summary of Portal the game for those who have not played so Eric's video may be more enjoyable...
You awake in a training area where you're given a neat gun that can create portals of course. You progress the levels guided by the voice of the master computer who at first seems to be congratulating you on your achievements. Soon you discover that "training" is using live ammo, and things the computer voice is telling you are not completely true. Training turns into "escaping with your life" by circumventing the normal training route. At the end when you think you've gotten rid of the computer, a terminal comes on and begins singing you this song. The computer is not completely gone after all......
Black Mesa is a reference to Apature Sciences' arch rival. It's also the base where the HalfLife saga begins.
Eric has materfully crafted his animation to retell the story of the song lyrics from an Amigan's point of view.
You can always hop over to youtube to see Portal videos too.
Plaz