when a band record a music video do they just perform then the actual track is played over them in the editing process, if this is so then the syncing must be very good and not out of time at all so they must have to do it loads to get it exactly in time with the album track?
I think Delboy3 is right on that one; I've seen a couple of "Making Of" videos and they've always had the music playing in the background. Maybe they mute it afterwards to get rid of background noise and the director shouting at them all and then sync' the original track onto the video.