Linear video editing

Linear video editing is a video editing post-production process of selecting, arranging and modifying images and sound in a predetermined, ordered sequence.^[1] Regardless of whether it was captured by a video camera, tapeless camcorder, or recorded in a television studio on a video tape recorder (VTR) the content must be accessedsequentially.^[2] For the most part video editing software has replaced linear editing.

Until the advent of computer-based random access non-linear editing systems (NLE) in the early 1990s "linear video editing" was simply called "video editing".

The first widely accepted video tape in the United States was 2 inch Quadruplex videotape and traveled at 15 inches per second. To gain enough head-to-tape speed, four video recording and playback heads were spun on a head wheel across most of the two-inch width of the tape. (Audio and synchronization tracks were recorded along the sides of the tape with stationary heads.) This system was known as Quad, for quadruplex recording.

The resulting video tracks were slightly less than a ninety-degree angle (considering the vector addition of high-speed spinning heads tracing across the 15 inches per second forward motion of the tape).

Originally, video was edited by visualizing the recorded track with ferrofluid and cutting it with a razor blade or guillotine cutter and splicing with video tape, in a manner similar to film editing. This was an arduous process and avoided where possible. When it was used, the two pieces of tape to be joined were painted with a solution of extremely fine iron filings suspended in carbon tetrachloride, a toxic and carcinogenic compound. This "developed" the magnetic tracks, making them visible when viewed through a microscope so that they could be aligned in a splicer designed for this task. The tracks had to be cut during a vertical retrace, without disturbing the odd-field/even-field ordering. The cut also had to be at the same angle that the video tracks were laid down on the tape. Since the video and audio read heads were several inches apart it was not possible to make a physical edit that would function correctly in both video and audio. The cut was made for video and a portion of audio then re-copied into the correct relationship, the same technique as for editing 16mm film with a combined magnetic audio track.

The disadvantages of physically editing tapes were many. Some broadcasters decreed that edited tapes could not be reused, in an era when the relatively high cost of the machines and tapes was balanced by the savings involved in being able to wipe and reuse the media. Others, such as the BBC, allowed reuse of spliced tape in certain circumstances as long as it conformed to strict criteria about the number of splices in a given duration. The process required great skill, and often resulted in edits that would roll (lose sync) and each edit required several minutes to perform, although this was also initially true of the electronic editing that came later.

In the USA, the television show Rowan & Martin's Laugh-In was the first and possibly only TV show to make extensive use of splice editing of videotape.