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Analog Protection System
The Analog Protection System (APS), also known as Analog Copy Protection (ACP) or Macrovision, is a VHS and DVD copy protection system originally developed by the Macrovision Corporation. Video tapes copied from DVDs encoded with APS become garbled and unwatchable. The process works by adding pulses to analog video signals to negatively impact the AGC circuit of a recording device. In digital devices, changes to the analog video signal are created by a chip that converts the digital video to analog within the device. In DVD players, trigger bits are created during DVD authoring to inform the APS that it should be applied to DVD players' analog outputs or analog video outputs on a PC while playing back a protected DVD-Video disc. In set top boxes trigger bits are incorporated into Conditional Access Entitlement Control Messages (ECM) in the stream delivered to the STB.
In VHS, alterations to the analog video signal are added in a Macrovision-provided "processor box" used by duplicators.
Analog video formats convey video signals as a series of raster scan lines. Most of these lines are used for constructing the visible image, and are shown on the screen. But several more lines exist which do not convey visual information. Known as the vertical blanking interval (VBI), these extra lines historically served no purpose other than to contain the vertical synchronizing pulses, but in more modern implementations they are used to carry or convey different things in different countries; for example closed captioning.
Macrovision's legacy analog copy protection (ACP) works by implanting a series of excessive voltage pulses within the off-screen VBI lines of video. These pulses were included physically within pre-existing recordings on VHS and Betamax and were generated upon playback by a chip in DVD players and digital cable or satellite boxes. A DVD recorder receiving an analog signal featuring these pulses would detect them and display a message saying that the source is "copy-protected" followed by aborting the recording. VCRs, in turn, react to these excessive voltage pulses by compensating with their automatic gain control circuitry. This causes the recorded picture to wildly change brightness, rendering it annoying to watch. The system was only effective on VCRs made in the mid-1980s. In addition, these voltage pulses caused some TVs to lose track of the vertical blanking interval, meaning they no longer knew when one frame ended and the next began. This caused the picture to roll wildly up and down the screen on affected sets.
A later form of Macrovision's analog copy protection, called Level II ACP, introduced multiple 180-degree phase inversions to the analog signal's color burst. Also known as color striping, this technology caused numerous off-color bands to appear within the picture.
APS can be also signaled digitally, in the CGMS-A bit field sent in the vertical blanking interval.
Historically, the original Macrovision technology was considered a nuisance to some specialist users because it could interfere with other electronic equipment. For example, if one were to run a video signal through a VCR before the television, some VCRs would output a ruined signal regardless of whether it is recording. This also occurs in some TV-VCR combo sets. Apart from this, many DVD recorders mistake the mechanical instability of worn videotapes for Macrovision signals, and so refuse to make what would be perfectly legal DVD dubs of legitimate video tapes, such as home movies. This widespread problem was another factor contributing to the demand for devices that defeat Macrovision. The signal has also been known to confuse home theater line doublers (devices for improving the quality of video for large projection TVs) and some high-end television comb filters. In addition, Macrovision confuses many upconverters (devices that convert a video signal to a higher resolution), causing them to shut down and refuse to play Macrovision content.
APS was preceded by Copyguard, the very first embedded videotape copy protection process, in 1975. Copyguard was originally developed by Trans-American Video, Inc., and licensed to numerous early tape duplication houses. However, it notoriously problematic, with many legitimately purchased tapes triggering unstable pictures on some TV sets. It fell out of favor by the early 1980s, with APS replacing it as the new de facto standard.
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Analog Protection System
The Analog Protection System (APS), also known as Analog Copy Protection (ACP) or Macrovision, is a VHS and DVD copy protection system originally developed by the Macrovision Corporation. Video tapes copied from DVDs encoded with APS become garbled and unwatchable. The process works by adding pulses to analog video signals to negatively impact the AGC circuit of a recording device. In digital devices, changes to the analog video signal are created by a chip that converts the digital video to analog within the device. In DVD players, trigger bits are created during DVD authoring to inform the APS that it should be applied to DVD players' analog outputs or analog video outputs on a PC while playing back a protected DVD-Video disc. In set top boxes trigger bits are incorporated into Conditional Access Entitlement Control Messages (ECM) in the stream delivered to the STB.
In VHS, alterations to the analog video signal are added in a Macrovision-provided "processor box" used by duplicators.
Analog video formats convey video signals as a series of raster scan lines. Most of these lines are used for constructing the visible image, and are shown on the screen. But several more lines exist which do not convey visual information. Known as the vertical blanking interval (VBI), these extra lines historically served no purpose other than to contain the vertical synchronizing pulses, but in more modern implementations they are used to carry or convey different things in different countries; for example closed captioning.
Macrovision's legacy analog copy protection (ACP) works by implanting a series of excessive voltage pulses within the off-screen VBI lines of video. These pulses were included physically within pre-existing recordings on VHS and Betamax and were generated upon playback by a chip in DVD players and digital cable or satellite boxes. A DVD recorder receiving an analog signal featuring these pulses would detect them and display a message saying that the source is "copy-protected" followed by aborting the recording. VCRs, in turn, react to these excessive voltage pulses by compensating with their automatic gain control circuitry. This causes the recorded picture to wildly change brightness, rendering it annoying to watch. The system was only effective on VCRs made in the mid-1980s. In addition, these voltage pulses caused some TVs to lose track of the vertical blanking interval, meaning they no longer knew when one frame ended and the next began. This caused the picture to roll wildly up and down the screen on affected sets.
A later form of Macrovision's analog copy protection, called Level II ACP, introduced multiple 180-degree phase inversions to the analog signal's color burst. Also known as color striping, this technology caused numerous off-color bands to appear within the picture.
APS can be also signaled digitally, in the CGMS-A bit field sent in the vertical blanking interval.
Historically, the original Macrovision technology was considered a nuisance to some specialist users because it could interfere with other electronic equipment. For example, if one were to run a video signal through a VCR before the television, some VCRs would output a ruined signal regardless of whether it is recording. This also occurs in some TV-VCR combo sets. Apart from this, many DVD recorders mistake the mechanical instability of worn videotapes for Macrovision signals, and so refuse to make what would be perfectly legal DVD dubs of legitimate video tapes, such as home movies. This widespread problem was another factor contributing to the demand for devices that defeat Macrovision. The signal has also been known to confuse home theater line doublers (devices for improving the quality of video for large projection TVs) and some high-end television comb filters. In addition, Macrovision confuses many upconverters (devices that convert a video signal to a higher resolution), causing them to shut down and refuse to play Macrovision content.
APS was preceded by Copyguard, the very first embedded videotape copy protection process, in 1975. Copyguard was originally developed by Trans-American Video, Inc., and licensed to numerous early tape duplication houses. However, it notoriously problematic, with many legitimately purchased tapes triggering unstable pictures on some TV sets. It fell out of favor by the early 1980s, with APS replacing it as the new de facto standard.