Film series that steps out
A look at musicals famous - and obscure
When we think of the American movie musical, we think of its perfect moments. Gene Kelly singin’ in the rain. Fred Astaire and Ginger Rogers dancing cheek to cheek. Busby Berkeley’s insane terpsichorean fractals. ArtsEmerson’s five-month film series “Gotta Dance: A Survey of the American Film Musical’’ has those moments and more, but it’s more welcome for rescuing a number of rarely-seen and hardly-ever-seen early film musicals and bringing them to the Bright in restored prints.