Analog Protection System

This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. Find sources: "Analog Protection System" – news · newspapers · books · scholar · JSTOR (April 2024) (Learn how and when to remove this message)

The Analog Protection System (APS), also known as Analog Copy Protection (ACP), Copyguard or Macrovision,^[1] is a VHS^[2] 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.