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Copy Protection For Video Tape
How does copy protection work on a video tape?
Making illegal copies of video tapes has always been a major
concern to those who market them. In a recent study conducted by them it was estimated that over 30% of VCR households had unauthorized copies, and that the total annual revenue loss due to copying is estimated at $370,000,000 annually. Consequently, copy protection on video tapes (typically Macrovision) is a big thing.
How it works is actually a pretty simple thing. It's not that the
second VCR knows that the video signal is coming from a
video tape. It's that the signal coming from the original video tape contains a special type of noise that the TV set doesn't notice, but that a VCR cannot handle. This noise signal confuses a component, known as an automatic gain control (AGC) circuit, in the VCR, and the confused AGC records the signal incorrectly. Of course, there are after market devices that can compensate for this (often marketed as "video enhancers").
In "Cliff Hanger" when the girl is dangling off Stallone’s arm, the camera flashes to the chopper and the old man in the picture is laughing.
Drama is life with the dull bits cut out. ~Alfred Hitchcock
