CGMS-A

Copy Generation Management System - Analog (CGMS-A) is a copy protection mechanism for analog television signals. It consists of a waveform inserted into the non-picture Vertical Blanking Interval (VBI) of an analogue video signal. If a compatible recording device (for example, a DVD recorder) detects this waveform, it may block or restrict recording of the video content.

It is not the same as the broadcast flag, which is designed for use in digital television signals, although the concept is the same. There is a digital form of CGMS specified as CGMS-D which is required by the DTCP ("5C") protection standard.

CGMS-A has been in existence since 1995, and has been standardized by various organizations including the IEC and EIA/CEA. It is used in devices such as PVRs/DVRs, DVD players and recorders, D-VHS, and Blu-ray recorders, as well certain television broadcasts. More recent TiVo firmwares comply with CGMS-A signals.

Implementation of CGMS-A is required for certain applications by DVD CCA license. D-VHS and some DVD recorders comply with CGMS-A signal on analog inputs. The technology requires minimal signal processing.

Where the source signal is analogue (e.g. VHS, analogue broadcast), the CGMS-A signalling may be present in that source.

Where the source signal is digital (e.g. DVD, digital broadcast), then the Copy Control Information (CCI) is carried in metadata in the digital transport or program stream, and a compliant hardware device (e.g. a DVD player) will read that data, and encode it into the analogue video signal generated within the device itself.

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