The "play it in ..." line may have just been something that one would commonly hear in public places in earlier eras. Real piano bars in the speakeasys, where customers would sing, apparently were much more common once upon a time - although that may be just a fairy tale.
So far as I know, it was never common to record the sound and the pictures at the same time, and even in the old days clipping a few frames from the picture part may have caused the techs to speed up or slow down the sound to maintain synch, which means that you can't usually tune to a movie - or to many current commercial CDs for that matter. Standin "voices" were (and probably are) used a lot, so the voice you hear often is not the voice of the actor/actress who played the part.
Real "bloops," like the naked "Invisible Man" leaving tracks of shoes, are something of an embarassment to the movie folk, but no one was ever concerned that no "barber" in any movie ever made knew how to strop a razor.