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Macrovision
- Anti-Copy Process - DVD
Macrovision copy protection is the only tool available in the DVD
format to prevent unauthorised copying to VCR's. It is activated
during DVD authoring, by setting certain Macrovision copy protection
control bits to 'ON'. When a disc with these bits set is played
back on a DVD player, the digital-to-analogue converter chip within
the DVD player applies Macrovision copy protection to the outgoing
analogue video signal, causing VHS copies made to be substantially
distorted, whilst having no effect on original viewing whatsoever.
The actual copy protection signal applied to DVD programming is
comprised of two elements: Automatic Gain Control (AGC) and Colourstripe.
The AGC process, which has been used to protect pre-recorded video
cassette since 1985, consists of pulses placed in the vertical interval
that TV's cannot detect. When a copy is attempted, the pulses confuse
a VCR's record circuitry, causing copies to exhibit characteristics
such as dim and/or noisy pictures, loss of colour, loss of video
and picture tearing etc. The Colourstripe Process consists of changes
to colourburst information that are transparent on original viewing,
but that produces annoying lines across the picture on any illegal
copy during playback. Used together, these technologies provide
the world's most effective defence against unauthorised copying.
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