Most picture tapes come with acopy auspices signalembedded on the mag tape . One democratic product in this arena is made byMacrovision . fit in to Macrovision , " The applied science is applied to over 550 million videocassette annually and is used by every MPAA picture show studio on some or all of their videocassette release . Over 220 commercial-grade duplicate facilities around the world are fit out to supply Macrovision videocassette copy protection to rights possessor . " Also , " The study found that over 30 % of VCR households include to having wildcat copies , and that the full one-year revenue loss due to copying is estimated at $ 370,000,000 per year . " So , it ’s a reasonably big problem .
The room the transcript protection signal works is interesting . It ’s not that the secondVCR"knows " that the video sign is coming from a video tape . It ’s that the signal come from the original video tapeline contain a peculiar type ofnoisethat theTV setdoesn’t bill but a VCR can not handle . This racket signal confuses a component , known as anautomatic gain control(AGC ) circuit , in the VCR , and the confused AGC records the sign incorrectly .
If you look at the HowStuffWorks articleHow Television workings , you will notice that a composite video signal contains luminance information ( how brilliant a picture element should look on the screen door ) , color information ( the color of each pixel ) , and synchronization information . The synchronization information tells the electron gun paint the epitome when to fritter away back to the left side of the screen on each scan line , and when to shoot back to the top of the screen at the remnant of each frame . These are calledhorizontal synchronization pulsesandvertical synchronicity pulses . There is a time period of clip , known as theblanking interval , when the electron hired gun of the telly is turn off while the negatron beam shoots back to the left or top of the screen .
The copy protective covering signal is enter in thevertical blanking separation , and it containsextra sync pulsesandfake video data . Since the television set is not display anything during the blank interval , nothing shows up on the screen . That ’s why it looks okay on the TV . A VCR , on the other hired hand , is trying to make a close recording of the total signal that it see . It therefore tries to record the signal containing the extra sync pulses . The AGC visualise the extra sync impulse and the fake video data point and sets its story wrongly as a final result . The real TV data in the frame gets recorded at a much lower level than it unremarkably would , so the CRT screen call on inglorious instead of showing the movie . You ’ll still hear the audio , however , because a wholly separate tour register the audio .
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