Linear editing

Linear video editing is a video editing post-production process of selecting, arranging and modifying images and sound in a predetermined, ordered sequence. 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 accessed sequentially.

For the most part video editing software has replaced linear editing. In the past, film editing was done in linear fashion, where film reels were literally cut into long strips divided by takes and scenes, and then glued or taped back together to create a logical sequence of film. Linear video editing is more time consuming and highly specialised and tedious work. Still, it is relevant today because of these reasons:
* The method is simple and inexpensive.
* Mandatory for some jobs: for example if only two sections of video clips are to be joined together in sequence it is often the quickest and easiest way.
* If video editors learn linear editing skills it increases their knowledge as well as versatility. According to many professional editors who learn linear editing skills first they tend to become proficient all-round editors.

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.

History

Live television is still essentially produced in the same manner as it was in the 1950s, although transformed by modern technical advances. Before videotape, the only way of airing the same shows again was by filming shows using a kinescope, essentially a video monitor paired with a movie camera. However, kinescopes (the films of television shows) suffered from various sorts of picture degradation, from image distortion and apparent scan lines to artifacts in contrast and loss of detail. Kinescopes had to be processed and printed in a film laboratory, making them unreliable for broadcasts delayed for different time zones.

The primary motivation for the development of video tape was as a short or long-term archival medium. Only after a series of technical advances spanning decades did video tape editing finally become a viable production tool, up to par with film editing.

Early technology

The first widely accepted video tape in the United States was two-inch quadruplex videotape and travelled 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
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