What is DVD?
What specifications are there for DVD?
What is DVD's capacity?
What capabilities does DVD Video have?

What is DVD?

DVD stands for "Digital Versatile Disc". It includes products and software built in conformance with a specification developed by a consortium of the largest computer, consumer electronics, and entertainment companies, including Matsushita, Philips, Toshiba, Sony, and Time-Warner.

What specifications are there for DVD?

Video Standards

The video standards being used include MPEG-1 and MPEG-2, with quality levels ranging from fixed-rate MPEG-1 at 30 fields per second at a resolution 352 x 240; to variable bit-rate MPEG-2 at 60 fields per second at a resolution of 720 x 480.

Audio Standards:

Audio standards include MPEG-1 stereo, MPEG-2 5.1 and 7.1 surround, Dolby AC-3 5.1 surround, and stereo ProLogic. Linear PCM at up to 24 bits per sample and 96 ksps in stereo is also specified. Audio sampling rate for MPEG-2 and AC-3 is defined as 48 ksps, not 44.1 ksps as in MPEG-1.

What is DVD's capacity?

Size:

The storage capacity of a single-sided, single-layer, 120 mm (5 inch) DVD is 4.7 gigabytes. This is often equated to 133 minutes of movie play time, assuming 3 audio streams and an arbitrary video quality/bit-rate of 3.5 megabits per second.

Data:

The data format for DVD Video discs allows for one video channel, but a large number of Program Chains that can access it in various ways. There can be up to 8 audio streams. Subpicture data, which are four-color graphics that can be used for subtitles, menus, etc., can be included in up to 32 channels which the user or title can select to play one at a time. There can be up to 99 title sets on a disc, with up to 999 Part_of_Title segments.

A typical combination of a MPEG-2 movie, three sound streams, and a few subpicture channels results in a play time on a single-sided disc of about 130 minutes; which is supposed to be sufficient to hold 95% of the movies made.

What capabilities does DVD Video have?

Compatibility:

One intended capability is wide ranging compatibility. DVD players are able to play any video disc on any TV system, PAL or NTSC, 5:4 screen or 16:9 screen. Players are compatible with Audio CD's and Video CD's. Other CD formats, such as Photo CD, CD-i, Sony Playstation, 3DO, etc. will be the option of the manufacturer. The intention is to appeal to users by combining the functions of presently separate audio and video entertainment machines (VCR and Audio CD) into a single entertainment player that can play the existing discs. It also takes advantage of the trend of integrated TV/multichannel audio "home theater" systems, which combine the audio and video presentation systems, and are ready for multichannel sound.

International:

DVD Video is designed with international compatibility in mind. It is capable of eight audio tracks, and 32 "subpicture" tracks (used for subtitles, menus, etc.); which can be used to put several selectable languages on each disc.

System Standard:

The DVD Video spec (Book B) describes the disc, the data format and contents on the disc, and the playback system. The advantages of a system specification are evident in the fact that over 600 million CD audio players have been sold, and billions of discs. A standardized system is cheaper to manufacture because all models are similar and designed to do a limited number of things as simply as possible; and they all work using any disc with any player. That is in contrast, for instance, to the current situation with CD-ROM's on PC's, where the majority of new titles don't work on the majority of existing computers.

Adjustable Aspect Ratios:

For maximum compatibility with different content material and display monitors, every player has the ability to select aspect ratios to best fit the monitor and video material being watched. Most movies have an aspect ratio (width/height) of 1.85, and some wide screen movies have aspect ratios of 2.25. Standard TV programs and TV sets have a ratio of 1.33 (4:3), as do 640x480 computer screens. There are new TVs with 16:9 screens (aspect ratio 1.78) that can display a standard size movie by chopping 2% of the width off each side.

1.85

2.25

1.33

1.78

For standard width TVs or any TV showing a wide screen movie, the options are to "pan and scan", squeeze, or "letter box" the movie. Squeezing looks silly, with everyone looking twelve feet tall. Pan and scan works sometimes because it can fill the screen with objects of interest, such as peoples' faces; but it has many problems, like when people are standing a distance apart in the movie and one of them doesn't fit into your picture.

DVD has special provisions to contain "center of interest" coordinates to tell the player how to crop the picture dynamically if you select to view the video in pan and scan mode. If you select letterbox mode, the scan lines are combined together so that every 4 lines results in 3 and a 360-line movie is displayed on the 480-line visible screen.

excerpted from "Frequently Asked Questions About DVD" by Kilroy Hughes, Future Media Systems, May 20, 1996.

"When it comes to technology, you're either part of the steamroller or part of the road." --Stewart Brand