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Macrovision video copy protection has existed for years. All consumer TV sets
made from the 1950s (TV), and from 1976 (VCR), through about 1998, (or until the newer ATSC
standard came along) are NTSC standard video devices.
The NTSC video standard (the broadcast standard used in North America and
Japan) is defined with a 525-line vertical resolution. However, only 480 of
those lines are used for transmitting video information. The extra 45 lines are
used to carry control codes (such as interlace information), closed captions,
and other similar non-video content. However, for this technology to work, the VCR that is used to make an unauthorized copy must contain the Automatic Gain Control circuitry, or no picture distortion will be witnessed. Macrovision estimates that 85% of the VCRs currently in use have automatic gain control circuitry in them, providing copy protection for nearly 550,000,000 videocassettes every year. Problems with MacrovisionThe most glaring problem with Macrovision is that compatibility is not guaranteed. Although the Automatic Gain Control circuitry is only supposed to affect the video signal when a Macrovision- protected video stream is recorded, many VCRs activate their video-scrambling chip when a signal is simply passing through the VCR.Since DVD players rarely include RF output (a single round cable with a single pin in the center - it looks like a cable TV connection), and millions of TVs currently in use lack composite video input (3 cables, 1 yellow for video and 2 (red and white) for audio - all have RCA-style connectors at the ends), or have only one set of composite inputs (which is occupied by a VCR, a Sony Playstation, or any of a variety of popular consumer electronics devices), many people discover that the only way to connect their brand-new DVD player to their television is to run the cables through their VCR (or use an RF modulator box). While there is nothing illegal about this configuration, due to poor design on the part of VCR manufacturers, quite a few people have been innocent victims of distorted pictures, and as DVD technology grows in popularity, this problem will grow exponentially. Already popular web sites are receiving questions from worried users, asking whether their new DVD player is broken because they are seeing an image that jumps around their television screen. The troubleshooting section of DVD player owner�s manuals rarely mentions this potential problem, incorrectly convincing many people that they own a faulty DVD player. While early adopters have been generally unaffected (due to the nature of early adopters, most own TVs with multiple S-Video or composite inputs, and thus do not need to connect their DVD players to their VCRs), this demographic is insignificant compared to the number of people who will try to connect their DVD players to their VCRs. In addition to improperly designed VCRs, some TVs are also incapable of resolving the Macrovision signal. Some Macrovision signals resemble bad synchronization pulses (the signals that tell the television where the electron guns should be at what time), and some TVs confuse these signals with real synchronization pulses. This problem primarily manifests itself with rental tapes having unstable pictures; however, it may also affect DVD. Alarmingly, this problem isn't restricted to older televisions - in fact, televisions produced after the widespread use of Macrovision copy protection are more likely to suffer from this problem than older TVs. Additionally, despite all the claims that DVD produces the best quality image
available, it is well known in technical circles that the image quality from
DVDs could be even better. Most TVs use a technique called interlacing: rather
than drawing each of the 480 visible scan lines every frame, only 240 are drawn
in an alternating pattern. Since DVD is a digital format, it is actually
possible to output all 480 scan lines at once, and on high-quality TVs (which
have Progressive inputs, in addition to composite and S-Video), such images are
much more stable than interlaced images. Enter the DMCAHistorically, problems with Macrovision have been circumvented easily. Because VCR manufacturers weren't required to include Automatic Gain Control circuitry in their products, several models can be purchased that conveniently ignore the Macrovision signals, and pass an uncorrupted signal to the television (these also allow unauthorized copying). Additionally, devices that defeat Macrovision protection are available for purchase at gray-market retailers (they are also fairly easy to make). While all of these choices could potentially stifle the copy-protection attempts, they do allow for correct, legitimate playback in cases where the owner's television or VCR is incompatible with Macrovision's signals.Unfortunately, due to the DMCA, such devices are no longer legal. On April 26, 2002, under section 1201k of the Digital Millenium Copyright Act, no analog video recording devices may be manufactured that do not contain Automatic Gain Control circuitry. Additionally, the sale, purchase, or manufacture of any device that disables Macrovision copy protection will be illegal under section 1201a of the Digital Millenium Copyright Act. |
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purpose of education and research.
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