Macrovision
Macrovision is an analog copy protection system which is maintained by the Macrovision Corporation of the same name .
The patents for the encryption and interference suppression methods are held by Macrovision .
Macrovision in VHS
The first copy protection process developed by Macrovision (1983) was used in the VHS video system . In order to meet the endeavors of the film industry to spread copy protection as widely as possible, the VHS standard developed in 1976 was expanded by JVC in 1985 to include the provision that VHS licensees are only allowed to build VHS recording devices with automatic gain control (AGC). Macrovision works purely analog by inserting a signal into the blanking interval of the recorded video signal on the cassette , which is intended to confuse the automatic gain control of the video recorder receiving during the copying process . This is achieved by recording a signal in a few lines of this area that switches between the sync pulse level (“blacker than black”) and a very bright white. This causes the video recorder to suspect that the signal is way too strong and will turn it down. If you record such a signal with a VHS recorder with AGC when making a copy, the copy is unusable due to strong and rapid fluctuations in brightness and / or synchronous interference. It is worth noting that VCRs of other formats are not susceptible to this Macrovision signal. Of course, the professional VHS recording machines that are used to record cassettes are just as unsusceptible - otherwise the original cassettes would not be playable correctly. The pure playback of Macrovision cassettes from the video recorder to the television works (with television sets since the mid-1980s) without interference, since the television sets are able to generate the return signal themselves using generators.
Macrovision on DVD
Macrovision is used in a different way on video DVDs . Unlike analog video cassettes, DVDs do not record the video signal itself, but only an encoded image content; the video signal is only generated in the playback device. The encoded picture content on a DVD does not contain any data for the blanking interval. Therefore, a Macrovisions signal cannot be stored on the DVD itself. Rather, the DVD only contains a flag (digital marking) that tells the player that it should insert a macrovision signal into the video signal that is generated. However, some DVD players always add the Macrovision noise regardless of whether there is a flag or not. Many DVD players can be made to ignore this flag by changing the firmware ; However, such a firmware change may no longer be carried out by companies in Germany for a fee.
Interference with some receiving devices
Since the Macrovision signal also contains points with the sync pulse level, it is interpreted by some devices as several picture lines, whereby the picture position is disturbed - the picture appears shifted upwards or it runs through. Older video projectors are particularly prone to this.
Some old televisions (built around 1980) also have problems with the Macrovision signal. Some manufacturers (e.g. Nordmende ) therefore set up special program slots for their television sets at the time, and when they were selected, the evaluation of the black level was modified.