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AACS consortium to require analogue signal restriction

In a deal reached this week after tense negotiations, the eight-company consortium behind the Advanced Access Content System, created for use by both next-generation DVD formats to prevent unauthorised copying, has agreed to require hardware makers to bar some high-definition signals from being sent from players to displays over analogue connections, Video Business reports.

It would appear that the analogue signal must be "down-converted" from the full 1920x1080 lines of resolution the players are capable of outputting to 960x540 lines-a resolution. While this represents 50% higher resolution than standard-definition DVD, it is only 25% the resolution of the full high-definition specs.

The players will be required to recognise and respond to a digital flag, called an Image Constraint Token, inserted into the movie data. If the flag is set to "on," the player must down-convert the analog signal. If set to "off," the player can pass the full high-def signal over the analog connections.

Whether particular movie is down-converted will be up to the studio.

Although movies in both Blu-ray and HD DVD will be encrypted while on the disc, the digital encryption is lost once the signal is converted to analogue, Video Business points out. Some studio executives take the view that down-converting the analogue signal from 1920x1080 lines to 960x540 lines would at least prevent pirates from starting with the highest-quality image.

As part of the deal with hardware makers, the studios will be required to disclose on a movie's packaging whether the image will be down-converted. Supporters of Image Constraint argue that few consumers will be able to tell the difference between down-converted analogue and high-definition.

Video Business reckons that many so-called HDTV sets are actually capable of displaying only 720 lines of resolution, regardless of the source, so viewers would not be getting full high-def anyway, even over digital connections. Once the analogue image is down-sampled to 540 lines, moreover, players will be permitted to use a signal processor to "up-convert" it to 720 or 1080 lines. Although such up-conversion does not restore the detail lost through down-sampling, it does improve overall picture sharpness.

Story filed 22.01.06

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