DVD - Digital Video Disc or Digital Versatile Disk - has generated a lot of media interest over the last year or so, but what exactly is it?
Although it looks like a standard CD-ROM, DVD has the potential to hold much larger amounts of data up to 17GB, compared with 680MB on a CD-ROM. Like a CD, the data is recorded on the disc as a series of tiny pits, and read back using a laser. However, the amount of data held has been increased in three ways:
The amount of data a DVD holds therefore depends on whether it is double or single sided, and double or single layer. A single layer, single sided DVD will hold 4.7GB, large enough to hold most Hollywood movies, 135 minutes of high resolution MPEG-2 video with up to eight channels of audio, providing much better audio than most current televisions can make use of. The double layer, single sided DVD will hold around 8.5GB. A double sided, double layer DVD will hold 17GB, and the first such disc was recently displayed by Imation (formerly 3M) at the DVD Forum in Brussels last September.
In addition to the increased storage, DVD will also transfer data at a much higher rate than the standard CD-ROM, 26.16mbit/s standard channel rate compared with 4.32 mbit/s.
The Consortium will also address compatibility issues, setting up neutral labs to test compatibility between different player brands and different discs. In Europe this testing will be organised by Phillips.
The biggest problem facing the Consortium has been finding a suitable copyright protection method. While copyright is an issue for computer software producers, it is much more of an issue for movie makers, causing some to believe that the way forward is for two different, incompatible drives, one supporting an anti-copy mechanism for movies, and another for DVD-ROM. On the 29 October 1996 the Copyright Protection Technical Working Group issued a number of copy protection principles. The movie industry had been pressing for a more comprehensive copy protection system, but bowed to pressure from the computer industry who felt such a system would place too high a burden on CPU power. The system proposed by IBM and Intel will encrypt only some of the frames of a movie. This will not scramble the picture entirely, but will reduce the quality sufficiently to make the movie unwatchable if it is illegally copied. A more sophisticated copyright system may be implemented at some point in the future. DVD-ROM players will not have to support the copyright protection scheme, though it is likely that most will, in order to advertise 'full DVD compatibility', and since initially most titles will be DVD-Movies.
To maintain backwards compatibility and ensure rapid uptake of DVD, all DVD players will read audio CDs and DVD-ROM drives will read existing CD-ROMs, except for current recordable CD-ROMs. Currently Kodak Photo-CDs are not supported, but it is likely that future DVD-ROM players would support them.
Long-term, DVD manufacturers are looking to replace video tape, and DVD offers a number of advantages, such as instant search and rewind and better quality audio and video than standard tape. Video tape however is cheap, readily available and recordable, and certainly until recordable-DVD is available video tapes market is unlikely to be threatened. This is not likely to be until after 2000. Currently the erasable format looks like it will be 2.6GB, and the write-once version 4.7GB. The write-once DVD-ROM players are likely be available sometime before erasable DVD-Video.
SIMA Multimedia Support Officer
Computer Graphics Unit
University of Manchester
Manchester M13 9PL
Tel: +44 161 275 6095
Fax: +44 161 275 6040