What happens in weeks of dance rehearsal before filming
Launch library · evergreen read

Long before cameras roll, a film song typically goes through weeks of rehearsal, starting with the choreographer working out core steps alone or with a small assistant team, before gradually bringing in the lead performers and only then the full ensemble of background dancers behind them.
Lead actors, who may have limited formal dance training, are often given extra individual sessions to build confidence and technique before joining group rehearsals, since a lead performer who looks unsure can undercut an otherwise polished sequence. Choreographers frequently simplify or adapt steps specifically to suit an actor's strengths.
Full run-throughs are rehearsed to the actual recorded track repeatedly, since timing precision only becomes second nature through sheer repetition. By the time filming begins, performers are expected to execute the routine so reliably that a director can call for multiple takes without steadily losing energy or accuracy.
This unseen rehearsal period, often far longer than the shoot itself, is where the real craft of a memorable dance number is actually built, quietly and repeatedly, over many days, well before a single camera has ever been switched on for the actual day of filming.