Anatomy of a Song (1976) is a half hour documentary (part two here) about Stephen Sondheim's song Someone in a Tree, from the musical Pacific Overtures. Sondheim talks about the challenges and thought processes behind what he calls his favourite of his own songs. See the original 1976 show in full here. Also see this earlier post on the same song.
SLYT of a Portuguese performance of the Wizard of Oz with a missing dance number added to the show.
Lord of the Rings...THE MUSICAL. You heard it here first, folks.