What does the black rectangle clipper when filming films and movies actually do? Why do they need one at all?

Question

I always wondered this

In: 133

Answer 1

the clapping sound is used to sync the audio to the video (they’re two separate recordings), allow you to sync the videos to each other if you have multiple cameras, and finally since you have it in frame anyway you can write the scene info on it for the editor to have on hand.