Pre-Digital Age Film Soundtracks

When listening to pop songs inserted into films before 1990 or so, it always struck me as odd that there were never any clicks and pops, indicating that the song was not copied off of a vinyl record. What was the method for directors to get songs onto their soundtracks before the digital age? Did they get permission from the label to copy the song's master tape directly onto their film's soundtrack?

 

They'd call up the label and have them run off a "1-to-1" 1/4" copy of the mono mix. That tape would come in and usually get transferred to 35mm mag, then mixed into the final film.

I can think of films where the soundtrack did come from vinyl, or at least came from very marginal tape. There were a lot more bad-sounding tracks in those days than most people remember, even going through the 1980s.