DVDs are continuing to take more market share from VHS sales and video entertainment businesses are making more shelf space for DVD titles at the cost of VHS shelf space. Clearly, DVD technology has been readily accepted by society.

For many people, when DVD is mentioned, the image of a movie comes to mind. In reality, there is a whole family of DVD formats available for ones use. This industry is still quite young and the depth of this industry isn't as extensive as the CD industry, but the DVD industry is growing at a very fast pace. This article is part 2 of a 3 part series and it will provide interesting historical facts about DVDs and will provide general information about the many DVD specifications and formats.

History

DVD, originally known as Digital Versatile Disc, was also labeled Digital Video Disc by the public after the popularity of the DVD Video movies. The architectural roots of DVDs are the same as CDs that were described in part one of this series. A DVD is a spin-off of the CD evolutionary path. The following are some interesting benchmark dates that marked the evolution of DVD technology to the present day DVDs [1].

1993 DDCD Double Density CDs introduced by Nimbus Technology proposed to increase the number of tracks by reducing the track width.

1994 DDCD Double Density CDs introduced by Optical Disc Corp also proposed to increase the number of tracks by reducing the track width.

1994 The MMCD introduced by Sony and Philips was a single-sided dual layer CD.

1995 The SDCD Super Density CDs introduced by Toshiba and Times-Warner was a double-sided CD.

1996 DVD technology introduced.

1997 DVD Players/Movies hit consumer markets.

1997 DVD-R (3.9Gig) standard created.

1998 DVD-Ram, DVD-Recordable system hit the market.

1998 DVD-Video/Rom authoring tools released to markets.

1999 DVD-Video becomes widely accepted.

1999 Second Generation DVD burners released.

1999 DVD-R (4.7Gig) media developed.

Your A B Cs

Specifications for CD formats were laid out in books identified by specific color designations. Specifications for DVD formats are designated by letters of the alphabet. Listed below are the 6 books that specify the various DVD formats [2] as sanctioned by the DVD Forum. It should be noted that there are DVD formats introduced by the DVD+RW Alliance that are not sanctioned by the DVD Forum and those formats will be described later.

Book A, DVD-Rom This book specifies the requirements for all industry-stamped DVD-Rom. This book details the Physical Layer (describes the physical dimensions of the track, pits, etc.), the Logical Layer (describes the logical constructs of the physical layer into sectors/blocks, etc). Interestingly, the Application layer has not been specified yet, thereby leaving the data format open and unrestrictive. This means any DVD disc can play on any DVD drive, but the data content of the disc may not be in a form readable for the playback system. This specification also details single-side single-layer disc, single-side double-layer disc, double-side single-layer disc and double-side double-layer discs.

Book B, DVD Video The Physical and Logical Layers for DVD-Video is identical to DVD-ROMs. This book specifies the Application layer for all DVD-Video and clearly defines video codex, audio compression, navigational commands, auxiliary files and other files it may contain. This specification is the most restrictive of all DVD specifications and further defines MPEG2 variable bit rate video, alternate camera angles, multiple aspects ratios, and interactive menus with chapter breaks, parental, presentation and navigational controls. Sound specifications include Dolby AC-3, MPEG2, or linear pulse coded modulation (PCM) audio, Stereo or Surround Sound, up to 8 sound tracks (for foreign languages) and 32 sub-pictures streams for subtitles. And of course, digital to analog copy protection and content scrambling system (CSS) to prevent digital-to-digital copying.

Book C, DVD Audio This was the last specification to be approved after significant debate. This book specifies a wide variety of audio format. This disc supports the same high-definition multi-channel audio recording in Dolby Digital and DTS audio formats used in DVD-Video discs which means this disc will play on the home theater DVD player. The full potential of these discs lie in the increased quality of PCM audio format where the range of frequencies are more than 4 times that of today's CDs. This format makes available 24bit samples sizes and 192 KHz sample rate yielding a frequency response of 0 to 96 KHz and a dynamic range of 144dB. [3]

Book D, DVD-Recordable The DVD-R is a write-once recordable format. This format follows the Physical and Logical layer specified in Book A; however, the Application layer is not specified and is left to the user application. This book also specifies the recording media requirement, laser energy and wavelength for DVD-R discs. Current implementation utilizes the single-sided single-layer disc with plans to implement dual layer discs when technology becomes available.

Book E, DVD-Ram This book specifies the recording media (usually phase change technology) laser energy and wavelength for DVD-Ram discs with potential for 100,000 rewrites per disc. Traditional DVD-Ram were housed in a cartridge that could not be opened, making them incompatible with most present day DVD readers or players. Type II and Type IV cartridges could be opened and the disc removed so the disc could be played in DVD-Ram-compatible DVD readers or stand-alone players. The first disc introduced was the single-sided 2.6 GB or 5.2 GB double-sided. Later versions increased the size to 4.7GB single-sided or the 9.4 GB double-sided discs. Current phase change technology seems to preclude double layer implementations.

Book F, DVD-RW The DVD-RW is a rewriteable format and is compatible with most later-model readers and burners. This format follows the Physical and Logical layer specified in Book A; however, the Application layer is not specified and is left to the user application. The recording media (usually phase change technology) and can typically be rewritten 1000 times. Current phase change technology seems to preclude double layer implementations. [4]

DVD Formats

Most DVD formats are sanctioned by the DVD Forum, the official body for providing specifications. However, the DVD+RW Alliance has introduced to the market other DVD formats that are not sanctioned by the DVD Forum and they are listed here with the other typical DVD formats. The following will list most of the commonly known formats along with a brief description of their application.

DVD-Audio Book C specification. This DVD provides for High Fidelity sound and requires equipment designed to decode and play this format. User level sound capture and editing applications are not readily available to burn DVD-R or DVD-RW discs in this format; therefore, most DVD Audio discs are commercially manufactured.

DVD-MP3 Book A, D or F specification. The DVD disc with MP3 Application layer can be manufactured or burned by the user.

DVD-R Authoring Book D specification, version 1 & 2. Version 1 specifies differences in the physical layer by specifying larger pit length and wider track spacing yielding 3.9 GB, where the Version 2 with smaller pit length and tighter track spacing yields 4.7 GB. Many high-end professional burners use the more expensive DVD-R Authoring disc; one reference indicated that once burned, the disc can be read on any type of reader/player. This is confusing in that the physical dimensions of the pits and tracks of the version 1 disc are different than the version 2 disc. For this to work, the players have to be able to detect the different physical characteristics and then decode respectively.

DVD-R General Book D specification version 2. Most consumer DVD-R burners use the cheaper 4.7 GB DVD-R General disc.

DVD+R Format introduced by the DVD+RW Alliance. This disc is very similar in design, usage and compatibility to the DVD-R disc. Later model DVD burners are generally compatible with both formats if they meet the DVD Forum standard "DVD Multi Records".

DVD-Ram Book E specification. This format requires special writers. The DVDs are housed in a cartridge and later versions of the cartridge can be accessed so the DVD can be removed and played in a compliant DVD reader.

DVD-RW Book F specification. This is the rewritable format. Generally, the recording media is phase change technology that permits up to 1000 rewrites.

DVD+RW Format introduced by the DVD+RW Alliance. This format is very similar in design, usage and compatibility with DVD-RW. This format does offer several features not available to DVD-RW, like not having to rewrite the entire disc if you need to replace just a portion of the data, faster minimum write speeds, background formatting and constant angular velocity CAV, best for raw data transfers necessary for video/ audio applications, and constant linear velocity CLV mode for quicker access to data. [5]

DVD-R/W Appears to be synonymous with DVD-RW, although one report indicated it was the name used for RW technology prior to the issuance of the DVD-RW standard.

DVD+R/W Appears to be synonymous with DVD+RW although one report indicated it was the name used for RW technology prior to the issuance of the DVD+RW standard.

DVD-Rom Book A specifications. These are manufactured DVD discs, where typical applications and usages include games, video, audio, database and some earlier movies.

DVD-SVCD Book D or F specification. This is a specialized application format on top of a DVD-R or DVD-RW disc. This format is generally used to pre-author SVCD prior to production.

DVD-VCD Book D or F specification. This is a specialized application format on top of a DVD-R or DVD-RW disc. This format is generally used to pre-author VCD prior to production.

DVD-Video Book B specification. This is the typical format used for the DVD movies.

DVI Book A, D or F, Digital Video Interactive. DVI is similar to the CD-Interactive disc, where data, video and images are presented and some user interactivity is required. This format has similar usages as the CD-I in education and industry for education and training.

DIVX A defunct DVD video rental format owned and promoted by Circuit City. Format required a phone line to be connected to the player at all times and you had to rent the movie for around $5.00 for 48 hour viewing time.

What is Next?

Next month, in the final part of this series, CD and DVD data will be pulled together in a comparison, and information will be presented on future CD and DVD products.