Linear video editing

Linear video editing is the process of selecting, arranging and modifying the images and sound recorded on video tape whether captured by a video camera or recorded in a studio. Until the advent of computer based non-linear editing in the early 1990s "linear video editing" was simply called “video editing” .

Television was basically a "live" medium until the introduction of videotape. "Editing" was performed by "switching" from amongst two or more cameras, with much the same effect as film edits. The first widely-accepted videotape in the United States was 2 inches wide and travelled at 30 inches per second. To gain enough head-to-tape speed, 4 video recording and playback heads were spun on a head wheel 'across' most of the 2 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.

The resulting video tracks were slightly less than a ninety-degree angle (considering the vector addition of high-speed spinning heads tracing across the 30 inches per second forward motion of the tape).

Originally video tape was edited by physically cutting and splicing the tape, in a manner similar to film editing. This was an arduous process and not widely performed. 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 tetracloride. This exposed the magnetic tracks, 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 the video tracks were laid down on the tape.

The television show Rowan & Martin's Laugh-In was the first and possibly only TV show to make extensive use of this method.

A system for editing Quad tape "by hand" was developed by the 1960s. It was really just a means of synchronizing the playback of two machines so that the signal of the new shot could be "punched in" with a reasonable chance at success. One problem with this and early computer-controlled systems was that the audio track was prone to suffer artifacs (i.e. a short buzzing sound) because the video of the newly-recorded shot would record into the side of the audio track. A commercial solution known as "Buzz Off" was used to minimize this effect.

For more than a decade, computer-controlled Quad editing systems were the standard post-production tool for television. Quad tape involved expensive hardware, time-consuming setup, relatively long rollback times for each edit and showed misalignment as disagreeable "banding" in the video. That said, it should be mentioned that Quad tape has a better bandwidth than any smaller-format analogue tape, and properly handled could produce a picture indistinguishable from that of a live camera.

When helical scan video recorders became the standard it was no longer practical to physically cut the tape. At this point video editing became a process of using two video tape machines, playing back the source tape (or raw footage ) from one machine and copying just the portions desired on to a second tape (the edit master ).

The bulk of linear editing is done simply, with two machines and a device to control them. Many video tape machines are capable of controlling a second machine, eliminating the need for an editing control device.

Video editing reached its full potential in the late 1970s when computer-controlled edit suite controllers were developed, which could orchestrate an edit based on an edit decision list (EDL), using timecode to synchronize multiple tape machines and auxiliary devices. The most popular and widely used computer edit systems came from Sony, Ampex and the venerable CMX. Systems like these were expensive, (especially when considering auxiliary equipment like VTRs, video switchers and graphics generators) and were usually limited to high-end post-production facilities.

While computer based non-linear editing has been adopted throughout most of the commercial, film, industrial and consumer video industries, linear video tape editing is still commonplace in television station newsrooms and medium sized production facilities which haven’t made the capital investment in newer technologies.

The widespread availability of videotape editing led to the music video boom of the 1980s.

Links:

Web Site: The Museum of Early Video Editing Equipment and Techniques, April 11, 2005: URL: http://www.sssm.com/editing/museum/

Web Site: Helical Scan, A Whatis.com definition, April 11, 2005. URL: http://searchstorage.techtarget.com/sDefinition/0,,sid5_gci214473,00.html