DVD (Digital Versatile Disk) (page 6)

DVD-ROM

Like a CD, a DVD-ROM is a pre-recorded disk. DVD-ROM is used to store general data, as well as video and audio information needed for multimedia applications and computer games. DVD-ROM satisfies the following requirements:

Backward compatibility with CD-ROMs
Forward compatibility with the future recordable (R) and rewritable (RW) disks
Single format for computer and TV applications
Single file system for all data types and media types

The backward compatibility of the DVD drives means that it will read both CD-ROM and CD-audio, which makes them a great replacement for CD-drives. Because of higher bit density and other advantageous features, even a 5x-speed DVD drive will read the CD at the rate equivalent to about 40x for the regular CD drive. For now, DVD drives are, in general, more expensive, and require special MPEG-2 hardware or software decoders to read the compressed data. To have the best video quality, the hardware approach is better unless the fastest processors are used.

This clearly makes DVD-ROM a computer storage of the near future, especially for databases, multimedia, games, interactive video, etc.

DVD-Videoand DVD-Audio

One of the reasons for the success of DVD technology is the DVD-Video formats. DVD video application is strongly dependent on data compression, since at the bit rate of 167 Mbps (which corresponds to the video rate specified by the CCIR-601 digital video standard), the 4.7 gigabyte capacity of a standard DVD would be enough to store roughly 4 minutes of digital video. This provides for the nominal 133 minutes of playing time for DVD-5. Longer movies should use a dual-layer technology (DVD-9). The data on the first layer start at the inside of the disk and end at the outside, where the data on the second layer start thus providing uninterrupted playback.

Two types of video compression standards could be used for DVD: MPEG-1 and MPEG-2, but only MPEG-2 video data can be copy protected and region coded (MPEG stands for the Moving Picture Experts Group). Therefore, the same techniques of copy protection as are currently used for CDs are being adopted for DVD.

Like all compression algorithms (WinZip is one example), MPEG-2 analyzes repetition in the video signal, called redundancy, and tries to get rid of it. MPEG-2 is capable of 'filtering' about 97% of the data in the video signal without significantly degrading the quality of the picture. This allows recording of 133 minutes on a 4.7 GB disk at a much lower bit rate than required by the digital video standard.

DVD-Video may have up to 8 (typically, three) tracks of mono, stereo, or multi-channel surround sound, which makes it much better than the VCR. The audio encoding formats include Dolby Digital (5.1 channel surround sound), MPEG (up to 7.1 channels), LPCM (number of channels is hardware dependent), and DTS (only in addition to one of the other formats).

DVD's direct data access allows interactivity and direct access to the movie episodes or other information of the disk. DVD also allows subtitles (up to 32 sets in different languages), making any DVD really universal. On the other hand, to provide additional copy protection, most DVDs have so-called regional coding, making it impossible to play the same disk in different regions, since most DVD-Videos are made for a specific region or country and not for free world-wide use. There are 6 regions (see next table) used for DVD-Video coding:

Region codes
1
2
3
4
6

Countries / Geographic regions
USA, Canada
Europe, Japan, Middle East, South Africa Southeast Asia, Taiwan
Australia, New Zealand, Central and South America, Mexico
Russia, India, Pakistan, Part of Africa
China

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