Diegetic and Non-Diegetic Sound

A diegetic sound is a sound heard within the world of the film. Everything the viewer hears within the world of the film therefore counts to be diegetic. An example of this is character dialogue or a car on the street sounding it's horn. Non-Diegetic sound is sound that as i like to say, takes over and floods over all other sounds. An example of this is the theme tune in James Bond. In many cases films merge the two in a bridge of music connecting a change of scene. Picture a man listening to the radio in his room and as you hear the flicker of his lighter whilst he lights his cigarette, the music becomes louder and almost takes over every other sound in the scene. The flicker of the lighter could be described as a bridge from diegetic to non-diegetic, and the non diegetic could be used to switch scenes.