Hollywood tunes into anti-piracy audio signals

Pirate DVDs made by copying movies in cinemas could become a thing of the past in the HD era, if technology presented to the DVD Forum proves successful.

The system requires film distributors to embed an inaudible watermark in film soundtracks. HD DVD players will contain a sensor that listens out for the watermark in the soundtracks of any disc being played.

Since official HD DVDs will not contain the watermark, its presence on the disc reveals the disc to be a pirate copy.

Playback will then be aborted, and the buyer's name and address beamed to the nearest law enforcement agency. Just joking.

The watermark comprises digital data encoded in subtle shifts in the audio waveform that makes up the soundtrack, New Scientist reports this week. Human ears can't detect the fluctuations.

Whether the pirates digitise a movie print directly, or simply point a camcorder at the cinema screen, they will still capture the audio and the watermark with it.

Legitimate DVDs will also contain a different watermark, Hollywood hopes, which can be used to look for content ripped from official discs, but that's going to be harder to square with established 'fair use' copying provisions in certain territories.

If the technique wins the approval of the DVD Forum, the presence of the watermark detector could be mandated in any player stamped with the official HD DVD brand. Of course, there will be plenty of machines out there whose manufacturers use the HD DVD logo without permission, or don't use it at all, and in either case may ship machines without the sensor.

However, Hollywood presumably believes it would nonetheless create a major disincentive for most consumers to buy pirate HD DVDs. Buy one that turns out not to work, and users may go on to buy a second disc. But they won't buy a third, the argument runs.

It is not clear at this stage whether the rival Blu-ray Disc format will adopt the technique. The system was detailed this week by a Warner Bros representative. Now that Warner is backing both BD and HD DVD, there's a good chance BD will incorporate the system. ®