Macrovision notable for its video copy-prevention scheme of the same name. A VHS videotape? or DVD (no laserdisc? or [video CD]? players implement it) encoded with macrovision will cause a VCR set to record it to fail. This is usually visible as a scrambled picture as if the tracking was incorrect or the picture will fade between overly light and dark.
This is achieved through a signal implanted within the offscreen range of the video signal either encoded directly on the tape (as with VHS) or implanted by a chip in the player (as with DVDs.) NTSC and other video formats store the video signal basically as "lines". A portion of these lines are used for constructing the visible image by transposing them on the screen, but there are a few lines outside the visible range that are used for things like closed-captioning and SAP alternate audio. This is the area that the Macrovision signal also resides. It is merely a garbled signal spike. The viewer on the screen sees nothing in ordinary use of the video because the signal is outside the visible area, but it does cause the automatic tracking and gain control of the recording VCR to constantly compensate, causing the video to become distorted.
Macrovision is a nuisance to some people because it can interfere with other electronic equipment. If one were to run their video signal through a VCR before the television, many VCRs will garble the signal regardless of whether or not it is recording. Because of Macrovision, it is often not possible to attach a DVD player to a TV which as a built-in VCR. The signal also confuses home theater line-doublers (devices for improving the quality of video for large projection TV's) and some high-end television comb-filters. And of course, United States fair-use law dictates that one is fully within their legal rights to copy videos they own.
Some DVD players give you the ability to shut macrovision off. There are also cheap devices for sale that filter out the macrovision spikes and thereby defeat the system. These products tend not to last long as Macrovision company often sues the manufacturer regardless of whether they reverse engineered the technology. The Macrovision system is owned by Macrovision and is defended vigorously.
It is the position of film and television studios that macrovision is necessary to prevent piracy and they are fully within their rights to add a block to someone exercising their fair-use rights. It is also however the position of these studios that one does not have any right to copy their own videos, and have attempted to lead the courts to rule the same.
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