Macrovision Demystified

Although Macrovision video copy protection has existed for nearly 15 years, it wasn't until the recent acceptance of DVD in mainstream consumer markets that its existence was felt at all.

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. Macrovision copy protection works by adding certain codes to these control lines that are interpreted by an Automatic Gain Control chip in a VCR to scramble the video signal if the video is being recorded. Videocassettes that are copied from Macrovision-encoded source material will frequently exhibit color loss, image tearing, variable brightness, and picture instability. Since TVs and video switch boxes do not have Automatic Gain Control circuitry, the Macrovision signals are ignored when the DVD player is connected directly to the television, or indirectly through an A/V switching receiver or switchbox.

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 Macrovision

The 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. While there is nothing illegal about this configuration, due to pour 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. DVDs implement Macrovision by attaching a small code to the video stream indicating whether or not to enable Macrovision protection. Then, when the DVD player outputs the frame, it adds Macrovision codes to the frame; however, due to technical limitations, it has proven extremely difficult to create a DVD player that can output 480 scan lines per frame in addition to Macrovision control codes. Because this could potentially allow unscrupulous users to connect their DVD players to computer-based recording devices and create perfect copies, the MPAA and DVD Copy Control Association (DVD CCA) stalled the release of progressive-scan DVD players for nearly 18 months.

Enter the DMCA

Historically, 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, on October 26 of this year, 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.