Macrovision

Macrovision is a company that creates electronic copy prevention schemes. The name also refers to the video copy prevention scheme developed by that company.

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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 (excluding very old models, modified VCRs as well as those approved for "professional usage" ) . This is usually visible as a scrambled picture as if the tracking was incorrect or the picture will fade between overly light and dark.

Related Topics:
Videotape - DVD - Laserdisc - Video CD - VCR

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This is achieved through a signal implanted within the offscreen range (vertical blanking interval) of the video signal—either physically recorded directly on the tape (as with VHS) or created on playback by a chip in the player (as with DVDs).

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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 approximately 20 to 40 lines outside the visible range that are used for different things in different countries, like closed captioning and SAP alternate audio.

Related Topics:
NTSC - Closed captioning - SAP

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Macrovision inserts pulses into this non-displayed area. These signals cause the automatic gain control on the recording VCR to compensate for the varying strength. This makes the recorded picture wildly change brightness, rendering it unwatchable. On most televisions, the viewer on the screen sees no effect in ordinary playback use of the protected video because the signal is outside the visible area, but some TVs do not properly blank the vertical retrace and leave dotted white lines near the top of the picture. Some newer TVs also mistake the Macrovision pulses for synchronization pulses.

Related Topics:
Automatic gain control - TVs

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Another modification also used in Macrovision protection is the addition of colorstripes, rapidly modulated colorburst signals.

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Macrovision is a nuisance to some because it can interfere with other electronic equipment. If one were to run their video signal through a VCR before the television, some VCRs will output a ruined signal regardless of whether or not it is recording. This also occurs in some TV-VCR combo sets.

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The signal also confuses home theater line doublers (devices for improving the quality of video for large projection TVs) and some high-end television comb filters.

Related Topics:
Line doubler - Comb filter

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