Pop tunes are welcome in the movies, directors say, as long as it's in service of the plot

If you want to know what tunes will be on the next "Guardians of the Galaxy" movie, you don't have to wait until post-production — just visit director James Gunn during filming. For him, the music in his movies is so "baked in" he's playing it on set during shooting.

"With 'Guardian' movies, it...