The films of Betty Grable for 1948 through 1955 are not included in the List of Film Musicals by year. The musical film is a film genre in which songs sung by the characters are interwoven into the narrative, sometimes accompanied by dancing. The songs usually advance the plot or develop the film’s characters, though in some cases they serve merely as breaks in the storyline, often as elaborate “production numbers”. The musical film was a natural development of the stage musical after the emergence of sound film technology. Typically, the biggest difference between film and stage musicals is the use of lavish background scenery and locations that would be impractical in a theater. Musical films characteristically contain elements reminiscent of theater; performers often treat their song and dance numbers as if there is a live audience watching. In a sense, the viewer becomes the diegetic audience, as the performer looks directly into the camera and performs to it.