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.
Fred von Lohmann, an intellectual property attorney at the Electronic Frontier Foundation in San Francisco, California, says: "Few may object if you're only talking about the blue-laser DVD drives, but the trouble with watermarking schemes is the scope of the technology."
"For any watermarking scheme to be effective, technology companies have to be forced to re-engineer playback devices to detect the watermarks." "The risk is that Hollywood starts dictating the redesign of existing DVD drives, CD drives, hard drives, and personal computers, all to buttress the watermark."