An L cut, also known as a split edit, is an edit transition from one shot to another in film or video, where the picture and sound are synchronized but the transitions in each are not coincident. This is often done to enhance the aesthetics or flow of the film as L cuts allow the audience to see context (either before or after) of speaking rather than simply the speaking itself. Without L cuts, a conversation between two people can feel like a tennis match.
L cuts are also used to hide transitions between scenes. They can be very effective in editing dialog scenes shot with a single camera using multiple takes. The ability to cut the picture/video separately from the sound/audio allows the sound from the various takes to flow smoothly, even though the picture cuts are at different places. In longer shots, this allows the editor to use the picture from one take with the sound from another take if the dialog reading is better.
The name of the cut refers to the shape of the cut pieces of the film – the audio track is cut somewhat after (or before) the last frame of video, resulting in roughly L-shaped film ends, as the video and audio parts of film are in tracks, one below, one above, on the film itself.
A prominent example of an L cut occurs in the film The Silence of the Lambs when Clarice is leaving her first interview with Dr. Lecter. She has just been humiliated and remembers her father arriving home from work one day when she was a child; after he picks her up and spins her around, the camera pans over to a passing truck and tilts up to the sky. Then we hear Clarice’s sobs and cut back to her outside the mental institution, leaning on her car and crying.