Non-linear editing

Non-linear editing (NLE) is a form of offline editing for audio, video, and image editing. In offline editing, the original content is not modified in the course of editing. In non-linear editing, edits are specified and modified by specialized software. A pointer-based playlist, effectively an edit decision list (EDL), for video and audio, or a directed acyclic graph for still images, is used to keep track of edits. Each time the edited audio, video, or image is rendered, played back, or accessed, it is reconstructed from the original source and the specified editing steps. Although this process is more computationally intensive than directly modifying the original content, changing the edits themselves can be almost instantaneous, and it prevents further generation loss as the audio, video, or image is edited.

A non-linear editing system is a video editing (NLVE) program or application, or an audio editing (NLAE) digital audio workstation (DAW) system. These perform non-destructive editing on source material. The name is in contrast to 20th-century methods of linear video editing and film editing.

In linear video editing, the product is assembled from beginning to end, in that order. One can replace or overwrite sections of material, but never cut something out or insert extra material. Non-linear editing removes this restriction. Conventional film editing is a destructive process because the original film must be physically cut to perform an edit.

A non-linear editing approach may be used when all assets are available as files on video servers, or on local solid-state drives or hard disks, rather than recordings on reels or tapes. While linear editing is tied to the need to sequentially view film or hear tape, non-linear editing enables direct access to any video frame in a digital video clip, without having to play or scrub/shuttle through adjacent footage to reach it, as is necessary with video tape linear editing systems.

When ingesting audio or video feeds, metadata is attached to the clip. That metadata can be attached automatically (timecode, localization, take number, name of the clip) or manually (players' names, characters, in sports). It is then possible to access any frame by entering directly the timecode or the descriptive metadata. An editor can, for example, at the end of the day in the Olympic Games, easily retrieve all the clips related to the players who received a gold medal.

The non-linear editing method is similar in concept to the cut and paste techniques used in information technology (IT). However, with the use of non-linear editing systems, the destructive act of cutting of film negatives is eliminated. It can also be viewed as the audio/video equivalent of word processing, which is why it is called desktop video editing in the consumer space.

In broadcasting applications, video and audio data are first captured to hard disk-based systems or other digital storage devices. The data are then imported into servers employing any necessary transcoding, digitizing or transfer. Once imported, the source material can be edited on a computer using any of a wide range of video editing software.

The end product of the offline non-linear editing process is a frame-accurate edit decision list (EDL), which can be taken, together with the source tapes, to an online quality tape or film editing suite. The EDL is then read into an edit controller and used to create a replica of the offline edit by playing portions of the source tapes back at full quality and recording them to a master as per the exact edit points of the EDL.