Copy Protection

The unauthorised copying of pre-recorded video tapes by domestic users is a big problem. Nearly one-in-three US video households has two VCRs, which may be used for back-to-back copying -linking together two video recorders with copying cables and then dubbing from one machine to the other. A survey of 1,000 VCR households in the US found that one illegal copy is made for every four videos sold. More than 30 per cent of American VCR households have unauthorised copies of pre-recorded videos in their libraries.

The big name in the anti-copying market is California based Macrovision, whose eponymous system has become the de facto standard in the video industry. Since 1986, its system has been used to protect 2billion video cassettes from back-to-back copying, and each year, a further 400million video tapes are encoded with the system. In its original analogue form, the Macrovision system adds a series of electronic pulses to the vertical blanking interval (VBI). When a Macrovision-encoded video tape is played in a VCR, the resulting picture looks normal. But if the video tape is copied, the Macrovision pulses 'fool' the copying video recorder into reacting as if the video signal was much stronger than it actually is. The VCR compensates for this by recording a weak video signal on to the tape, which plays havoc with a television's playback and synchronisation circuits. The resulting picture may roll on-screen, lose colour or suffer from flashing.

Macrovision says its system is 90 per cent effective against known television and video combinations. Users of the Macrovision system include the Hollywood film studios - in the UK, for example, 60 per cent of sell-thro videos and 72 per cent of all rental video cassettes are Macrovision protected.

With the coming of digital, the need to prohibit illegal copying becomes even more pressing. Major feature films are shown on pay-per-view and subscription channels much earlier than they appear on free-to-air television and the lack degredations of analogue transmission video pirating could thrive. With the prospect of digital recorders around the corner, West Coast film distributors are requiring copy protection as a condition of transmission contracts.