Were they lip synching?
(don't scream-- just a question...)
Also, I have a question about the filming. Yes, it looks great, but I wonder how much of it was really filmed in front of that audience. They seem to get shots that require a camera right on stage (reaction shots, the camera moving into the action), and then suddenly there doesn't seem to be a camera there in long shots.
I'd guess they have re-shot extra footage or reaction shots. I'm just guessing, but it seems like they shot a lot of it like a movie, with stop-start shooting and a lot of post-editing.
It looks great, but I wouldn't consider it a true "filmed live performance" if that's true. Ah, who knows...