The Analog Protection System (APS), also known as Copyguard or Macrovision, is a VHS and

DVD The DVD (common abbreviation for Digital Video Disc or Digital Versatile Disc) is a digital optical disc data storage format. It was invented and developed in 1995 and first released on November 1, 1996, in Japan. The medium can store any kind ...

copy protection Copy protection, also known as content protection, copy prevention and copy restriction, describes measures to enforce copyright by preventing the reproduction of software, films, music, and other media. Copy protection is most commonly found o ...

system originally developed by

Macrovision TiVo Corporation, formerly known as the Rovi Corporation and Macrovision Solutions Corporation, was an American technology company. Headquartered in San Jose, California, the company is primarily involved in licensing its intellectual property ...

. Video tapes copied from

s 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 Video is an electronic medium for the recording, copying, playback, broadcasting, and display of moving visual media. Video was first developed for mechanical television systems, which were quickly replaced by cathode-ray tube (CRT) sy ...

are created by a chip that converts the digital video to analog within the device. In

DVD player A DVD player is a device that plays DVDs produced under both the DVD-Video and DVD-Audio technical standards, two different and incompatible standards. Some DVD players will also play audio CDs. DVD players are connected to a television to ...

s, trigger bits are created during

DVD authoring DVD authoring is the process of creating a DVD video capable of playing on a DVD player. DVD authoring software must conform to the specifications set by the DVD Forum. DVD authoring is the second step in the process of producing finished DVD ...

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 box A set-top box (STB), also colloquially known as a cable box and historically television decoder, is an information appliance device that generally contains a TV-tuner input and displays output to a television set and an external source of si ...

es 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

-provided “processor box” used by duplicators. Devices marketed as "Video Stabilizers", along with time base correctors,Archived a
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and th
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may be used to attempt removal of the Macrovision copy protection mechanism. Digital recording devices (DVD recorders) often disallow the recording if they detect a protection signal on the input. The unit may display an error message about the program being copy protected. APS can be also signaled digitally, in the CGMS-A bit field sent in the

vertical blanking interval In a raster scan display, the vertical blanking interval (VBI), also known as the vertical interval or VBLANK, is the time between the end of the final visible line of a frame or field and the beginning of the first visible line of the next fra ...

References

*Smart Computing Dictionary Entry, ''Analog Protection System'' (2005)
Welcome , Sandhills Global , Gather, Process, Distribute
*Macrovision, ''Analog Protection System: A Presentation to the Analog Reconversion Discussion Group'' (2003)
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{{Refend Digital rights management systems Compact Disc and DVD copy protection