From the YouTube description:
A steel ball (about 2.7 inch diameter, 20 pound) is rolling on an aluminum track, about 25 inches in diameter, placed horizontally. Three pendulums, about 45 inches long with tunable weights at the lower end, controls three horse-shoe magnets that the steel ball has to pass by on the track. Embedded in the track is a (mechanical) controlling/timing mechanism. It looks like a steel wire bent into a triangular track, 5 inches long. The ball rolls over it and pushes the wire down through a slot in the track. This affects one of the pendulums and regulates its swinging motion. The steel ball has not stopped revolving for months.
Curious? Here is a video showing how this machine might work behind the scenes. Even if this isn't the method used, I want to make one now!
Still curious? Here's a book that deals with the long history of perpetual motion machines, Perpetual Motion: The History of an Obsession
[ Thanks Christophe! ]