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| Macrovision
Another copy protection mechanism used to protect movies is called macrovision. In the case of DVD movies this is the primary defense against making a copy of the DVD using your VCR.
Your VCR has circuitry to automatically adjust the picture if the input signal is too dark or too bright. Since VHS tapes wear over time this correction ability can enhance the playback of a degrading tape. Macrovision protection takes advantage of this circuitry by adding fake bright and fake dark signals to the movie. Your VCR is tricked into adjusting the picture to correct these bright and dark signals. But remember, those were fake signals and the picture was fine... until the VCR tries to "correct" it. The end result is the movie will constantly alternate from really dark to really bright and be considered unwatchable by most people.
So, you are probably wondering how the movie plays fine on your TV. TVs don't include this correction circuitry and therefore just ignore these fake signals.
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Copyright 2005, Macrovision Copy Protection Explained
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