Oh, just one more thing (™ Columbo) about music licensing: what was the first movie that paid to use real recordings of popular music?
For many years, licensed recordings were almost never used in film (or television for that matter). If characters turned on the radio or played a record, it would usually be music that was directly written for the film by the composer. For example, Alfred Hitchcock's Rear Window uses only "source music" from radios, phonographs and pianos -- but nearly all of it was composed by Franz Waxman; you don't hear anyone putting on a record that actually existed. In Out of the Past, when Robert Mitchum and Jane Greer put on a record, it's a recording of the movie's main title theme by Roy Webb, which has also been played by a jazz band in another scene.
By the early '70s, with American Graffiti and other films, movies and television had changed their tune (bad pun intended); now if a record was playing in a scene, it would be a real record. In The Long Goodbye, Robert Altman and John Williams even parodied the old practice by having Williams' title song reappear as every single piece of source music in the film (including two radios playing different "recordings" of the same song); that's how out of date that practice had become.
While I'm not fond of the way pop recordings are often used in place of real soundtrack music, I think it is much, much better (though more expensive) to have real recordings whenever source music is called for. If someone is playing a record, it should be a real recording, not only for realism but because the character's choice of music tells you something about that character. But when did it become all right for studios to pay to use recordings that they didn't own?
The first movie I'm aware of that uses a clearly-identifiable popular recording (that wasn't created directly for the film) is Henry King's masterpiece Margie (1946). This movie is framed as a flashback to the '20s, and transitions from the present to the past by having Margie (Jeanne Crain) and her daughter put on "My Time Is Your Time" by Rudy Vallee. Most of the other '20s songs are performed by people in the film, but the use of "My Time Is Your Time" is more akin to what we'd expect today: a real period recording that the filmmakers paid to use.
But that's 1946, and there must be others before that. Are there? (I'm not talking about having people in the movie play or sing popular songs, like the bar pianist playing Rodgers and Hart's "The Blue Room" in The Big Sleep. I'm talking about actual recordings that had been made and released separately from the movie.)