Two more movies with mechanical music that I don't remember anyone
mentioning:

In "Easter Parade" Judy Garland sits down before a foot-pumper and
starts pumping to "I Love a Piano".  Amazingly the piano keeps on
playing when she stands up and starts dancing.

"Who framed Roger Rabbit" features a large band organ which Bob
Hoskins sings with and dances to towards the end.

I'm convinced that there's a music box sitting on the landing in
Frank Capra's "Arsenic and Old Lace" but it's never played so I can't
be sure.

Regards,

Eliyahu Shahar