Music and film alter our daily lives even if we don’t hear the music or see the film, because both change society; when those two forms meet perfectly, the union can spark a revolution. The first bombshell exploded around the turn of the 20th century.
Some people call them “silents,” but more properly, early films were “non-talkies,” because music, from a single piano to a full orchestra, accompanied every film, as much to cover the projector’s rattle as to add context. Birth of a Nation (1915) boasted the first score compiled specifically for a film; the first completely original score was for King Kong in 1933—these films’ major success was no coincidence. Song-and-dance film hits (think Fred Astaire) led to the translation of Broadway musicals onto the silver screen, where the soundtrack took center stage, as it were.