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

Let’s say that you are filming with multiple cameras from multiple angles. You may have also multiple microphones. When you snap the clapboard down, all the cameras and all the microphones record a spike of noise at the same time. When you go back later to edit, you take the footage from all the cameras and all the sound from the microphones and you can line them all up on that spike. This way you can edit between cameras (showing some from camera 1, then 3, then 2 …. and the sounds will still line up correctly without having to adjust very fine details manually.