Also known as source sound · source music
Sound that comes from inside the story's world, so the characters can hear it: dialogue, a car radio, a band in the room. Non-diegetic sound is added for the audience alone, like the score or a narrator talking to us.
On the page
Source music
A jukebox plays a slow country song.
The song cuts out mid-chorus.
The word comes from diegesis, Greek for narration, which film studies uses for the world of the story. The test is simple: could a character in the scene hear it? A song on the jukebox is diegetic; the strings that swell when the couple finally kisses are not.
On the page, diegetic sound belongs in action, because it is part of what happens: the radio plays, the phone rings, the crowd starts chanting. Name a specific song only when the scene turns on it, and expect it to change once rights are cleared. Leave the score out; it belongs to the composer and the edit.
The best moments sit on the line between the two. Music can start on a car radio and swell into score, or score can resolve into the record the hero lifts the needle from. A pre-lap carries sound across a cut. Write the shift you want the audience to feel in a sentence of action, and let post find the means.
V.O. versus O.S.: which screenplay extension should you use?
Use O.S. for a speaker who belongs to the current scene but is outside the frame; use V.O. when the voice comes from outside the scene's immediate physical action.
How to format a pre-lap in a screenplay
When the next scene's sound arrives before its picture, write it just above the scene it belongs to: a (PRE-LAP) cue for a line of dialogue, a PRE-LAP line in action for a sound.
How to format song lyrics in a screenplay
Set sung lines apart from speech — italics or all caps, one lyric line per line — and quote only the lyrics the scene actually needs.
Should sound effects be in all caps in a screenplay?
Capitalize a sound, prop, or action only when it has to jump off the page, and a speaking character's name at first appearance, so capitals still mean something.
Diegetic sound exists in the story's world, so the characters can hear it: dialogue, footsteps, a radio, a band. Non-diegetic sound is for the audience only: the score, a narrator speaking to us, effects added purely for emphasis.
Write music the characters hear when it matters to the scene, in action. Leave the score out. If a particular song is essential, name it once and be ready for it to change, because licensing decides what reaches the screen.
It depends on who can hear it. A narrator talking to the audience is non-diegetic: nobody in the scene hears the narration. A recording, a radio or a caller on speakerphone is diegetic, even though screenplays usually mark it V.O. too, because the speaker is not in the room. A character's thoughts sit between the two: they come from inside the story, but only that character hears them, which film studies calls internal diegetic sound. The extension says where a voice comes from; diegesis says who can hear it.
