
Sam S. answered 07/17/20
Directing and Assistant Directing w/ 10+ Years of Industry Experience
Hey there! Whenever you film scene involving sync of music with actions, dancing, and lyrics on-screen, production will use large speakers to playback the music. Usually this is done at a very high volume, much like in a concert, for the purpose of fully immersing the talent with the music they're performing to. In rare cases where permits for a location prohibits the loud playback and there's only one or a few actors/performers on-screen, production will provide talent with tiny wireless in-ear monitors to hear the music, but this is less common and not preferable to achieve the best performance.
The best method to sync the video back to the original music in post-production is to reference sync-audio recorded on set, either by recording in-camera or with a separate sound mixer and the clap of a slate at the beginning of a take.