Disaster movies

 作者:钭恃     |      日期:2019-03-08 04:11:02
By Barry Fox OVER 15 million homes around the world have unwittingly bought digital TV receivers which allow broadcasters to prevent them making watchable recordings of material they transmit. The news will surprise consumers who have invested in equipment to receive digital pay TV, only to find they can’t record the movie they have paid for and watch it later. Prerecorded VHS tapes have been copy-protected for the past decade. To do this the movie industry uses a system developed by the Californian company Macrovision. To make copy-proof tapes, manufacturers connect a Macrovision encoder between the master tape player and the slave decks that make authorised copies. The encoder adds extra pulses to the picture synchronisation pulses in the original signal. Analogue TVs need sync pulses to keep the pictures steady. When the tapes are played, TV sets ignore the extra pulses and display perfect pictures. But if the output of one VCR is connected to the input of another, to make an illicit copy of the tape, the extra pulses fool the recorder into making a copy which is too out of sync to play. However, this analogue anti-copy system cannot stop people making analogue copies of digital broadcasts, because sync pulses are not sent with the digital picture signal. Instead, the digital receiver adds its own sync pulses to the picture information. To protect material being broadcast in digital form, Macrovision has developed anti-copy circuitry that is built into the digital TV receiver. As the receiver converts the digital signal into analogue format for display on a conventional TV, the anti-copy encoder can add extra pulses to the output. A TV displays the pictures normally, but a VCR makes an unplayable copy. The encoder is switched on by trigger signals which the broadcaster transmits along with programmes which it does not want viewers to tape. Macrovision says the majority of digital receivers now being sold worldwide incorporate its anti-copy chips. In Britain, most receivers in the shops are fitted with the encoder chips, even though the terrestrial broadcaster On Digital is still negotiating with Macrovision. Jeremy Corcoran, Macrovision’s pay-per-view director says he hopes a deal will be signed soon. Meanwhile, satellite broadcaster BSkyB emphasises that it applies copy protection only to pay-per-view movies, and that subscription channels can be taped. But sceptical viewers will recall that free-to-air channels often become pay channels. For now, manufacturers can sell equipment that defeats Macrovision. But in the US,