In a café or restaurant scene, extras may move their lips without making a sound. This on-set instruction allows the dialogue and background chatter to be built separately.
An original version can combine dialogue recorded on set with lines re-recorded in a studio. What is post-synchronization for, and how do actors recapture their performances?
A slate, some numbers, and a sharp clap: the clapper helps you identify takes and synchronize sound with the image. Its usefulness carries over into editing, even when the shoot is digital.
