09:00 02 November 2005
All HD-DVD players will have a sensor that looks for inaudible watermarks in the soundtrack of movies. The watermarks will be included in the soundtracks of all major movies released to cinemas.
If a DVD player detects the telltale code, the disc must be an illegal copy made by copying a film print to video, or pointing a camcorder and microphone at a cinema screen. So the player refuses to play the disc.
The mark is made by slightly varying the waveform of speech and music in a regular pattern to convey a digital code. The variations are too subtle to be noticeable to the human ear, but are easily recognised by the decoder in the player.
A variation of the system can also prevent the playback of discs made by pointing a camcorder at a home screen while it is playing a legitimate disc sold to individual consumers.
The consumer discs will also have an audio watermark, which differs from the cinema mark. If an HD-DVD player senses the consumer watermark it will check whether the disc is a legal, factory-pressed version and, if not, shut down.
