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Macrovision

From Academic Kids

Macrovision is a company that creates electronic copy prevention schemes.

Macrovision is 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 (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.

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).

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.

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.

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. 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.

Contents

Legal Issues

Some DVD players give the user the option of disabling the Macrovision technology. This is possible since the signal is not stored on the DVD itself; instead commercial DVDs just contain an instruction to the player to create such a signal during playback. Some DVD players can be so configured as to pay no heed to such instructions.

There are also cheap devices called stabilizers, video stabilizers or enhancers for sale that filter out the Macrovision spikes and thereby defeat the system. Principle of their function lies in detecting the vertical synchronization signal, and forcing the lines occuring during the vertical blanking interval to black level, removing the AGC-confusing pulses. While their legality is unclear, they are common on the market. They can be even easily built by hobbyists, as nothing more than a cheap microcontroller together with an analog multiplexer and a little other circuitry.

The MPAA maintains it has every right to limit copying of movies, comparing DVDs to pay-per-view where the consumer is allowed to view the movie in question but nothing more. Many are concerned that the organization is attempting to quash fair use by disallowing consumers to make personal copies.

United States fair use law as interpreted in the decision over Betamax (Sony Corp. v. Universal City Studios) dictates that one is fully within their legal rights to copy videos they own, however the legality has changed somewhat with the Digital Millennium Copyright Act. In the US starting on April 26, 2002, no VCR may be manufactured or imported which does not contain the Automatic Gain Control circuitry (which makes VCRs vulnerable to Macrovision); this is contained in title 17, section 1201(k) of the Digital Millennium Copyright Act. There are a number of older VCR models that are not affected by Macrovision.

Furthermore, starting on October 26, 2001, the sale, purchase, or manufacture of any device that disables Macrovision copy prevention will be illegal under section 1201(a) of the same act. However, the constitutionality of many of the Act's provisions is under debate.

RipGuard

In February 2005, Macrovision introduced their new RipGuard technology. This is designed to prevent (or reduce) digital DVD copying by altering the format of the DVD content in such a way as to disrupt the ripping software. Macrovision claims (http://www.macrovision.com/products/ripguard/index.shtml) that 97% of all current DVD rippers will not be able to copy a DVD protected by RipGuard technology. The DVD backup scene however is adamant that a way to beat RipGuard will be found shortly after video DVDs are released which incorporate it. It should also be noted that every copy-protection scheme introduced by Macrovision to date has been circumvented.

On June, 2005, Macrovision sent a cease and desist letter to "Lightning UK!", the maker of DVD Decrypter (a program that allows users to backup their DVDs by bypassing CSS and Macrovision protection which can also be used for piracy). It is widely believed that this was due to the upcoming RipGuard and the likelihood that Lightning UK! would quickly find a method of circumventing this protection and incorporate it into DVD Decrypter.

Reference

See also

External links

fr:Macrovision

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