Why do they use a clapperboard?

Answer by  jogosamba (85)

A clapperboard synchronizes all of the cameras and audio recorders during a film shoot because each device sees or hears the clap at the exact same time.

Answer by  quisqualis (1756)

The clapperboard used in moviemaking is a clever device. It has a clapper on it so that technicians can tell whether the audio and video on a movie are perfectly synchronized. If they review a film take and find that the closing of the clapper and the clapper sound do not coincide, then they have some work to do.