A DVD disc can contain:
- DVD-Video (containing movies (video and sound))
- DVD-Audio (containing high-definition sound)
- DVD-Data (containing data)
- DVD-ROM (read only, manufactured by a press)
- DVD+R/RW (R=Recordable once, RW = ReWritable)
- DVD-R/RW (R=Recordable once, RW = ReWritable)
- DVD-RAM (random access rewritable)
The official DVD-Forum has created the DVD-R(W) standards. But as the licensing cost for this technology is very high, another group was founded, the DVD+R(W) standard created with lower licensing costs. Even so, DVD+R(W) media are more expensive then DVD-R(W) media.
The "+" and "-" are two similar technical standards that are partially compatible. Now half of the industry is supporting "+", and the other half "-". Only time will tell who wins this war against the consumer, and maybe even both standards will coexist in the longterm. It is predicted that most DVD readers in the future will be able to read both formats and some newer writers already write both formats.
Unlike compact discs, where sound (CDDA) is stored in a basically different way than data (ISO 9660), a properly authored DVD disc will always contain data in the UDF filesystem.
DVD-VideoDVD-Video discs require a DVD-drive with a MPEG-2 decoder (eg. a DVD-player or a DVD computer drive with a software DVD player). Commercial DVD movies are encoded using a combination of MPEG-2 compressed video and Dolby Digital audio (often in multi-channel formats.) Typical data rates for DVD movies range from 3-10 Mbit/s, and the bitrate is usually adaptive.
The audio data on a DVD movie can be of the format PCM, DTS, MPEG audio, or Dolby Digital (AC-3). In countries using the NTSC standard any movie should contain a sound track in PCM or Dolby AC-3 format, and any NTSC player must support these two, all the others are optional. This ensures any standard compatible disc can be played on any standard compatible player.
Initially, in countries using the PAL standard (most of Europe) the sound of DVD was supposed to be standardised on PCM and MPEG-2 audio, but apparently against the wishes of Philips, under public pressure on December 5, 1997, the DVD-Forum accepted the addition of Dolby AC-3 to the optional formats on discs and mandatory formats in players.
With several channels of audio from the DVD, the cabling needed to carry the signal to an amplifier or TV can occasionally be somewhat frustrating. Most systems include an optional digital connector for this task, which is then paired with a similar input on the amplifier. The selected audio signal is sent over the connection, typically over RCA jacks or TOSLINK, in its original format to be decoded by the audio equipment. When playing compact discs, the signal is sent in S/PDIF format instead.
Video is another issue which continues to present problems. Current systems typically include both composite video on an RCA jack, as well as s-video in the standard connector. However neither of these connectors were intended to be used for progressive video, so yet another set of connectors has started to appear in the form of component video, which fully separates the signal into its three components (whereas s-video has two, and composite only one). Additionally, the connectors are further confused by using a number of physical connectors, RCA or BNC, as well as using VGA cables in a non-standard way (VGA is normally RGB). Even worse, there are often two sets of component outputs, one carrying interlaced video, and the other progressive.
DVD Video may also include subtitles in various languages. They are stored as images with transparent background.
DVD Video may contain Chapters for easy navigation (and continuation of a partially watched film).
SecurityMost DVD-Video titles use Content Scrambling System (CSS) encryption, which is intended to discourage people from making perfect digital copies to another medium or from bypassing the region control mechanism (see below). Discs can also specify that the player use Macrovision, an analog anti-copying mechanism that prevents the consumer from copying the video onto a VCR tape. This alone would not prevent the duplication of DVD discs in their entirety without decrypting the data, given suitable equipment, although "consumer-grade" DVD writers deny this ability by refusing to duplicate the tracks on the disk which contain the decryption keys.
The CSS system has caused problems for the inclusion of DVD players in strictly open source operating systems, since open source player implementations can not officially obtain access to the decryption keys or license the patents involved in the CSS system. Proprietary software players may also be difficult to find on some platforms. However at least one successful effort has been made to write a decoder by reverse engineering, resulting in DeCSS. This has led to long-running legal battles and the arrest of some of those involved in creating or distributing the DeCSS code, through the use of the U.S. Digital Millennium Copyright Act, on the grounds that such software could also be used to facilitate unauthorised copying of the data on the discs.
Region codesDVD movies can contain a region code, denoting which area of the world it is targeted at, which is completely independent of encryption. The commercial DVD-video player specification dictates that players must only play discs that contain their region code. This allows the film studios to set different retail prices in different markets and extract the maximum possible price from consumers. With region coding, studios can dictate release schedules and prices around the world. However, many DVD players allow playback of any disc, or can be modified to do so. Region coding pertains to regional lockout, which originated from the video game industry.
|Playable in all regions
|United States, Canada, and U.S. territories
|Europe, Greenland, South Africa, Lesotho, Swaziland, Japan, Egypt, and the Middle East
|Southeast Asia, South Korea, Hong Kong, Indonesia, Philippines, Taiwan
|Australia, New Zealand, Mexico, Central America, South America
|Russia, other former Soviet Union countries, eastern Europe, Indian subcontinent, Mongolia, the rest of Africa
|People's Republic of China
|Reserved for future use
|International venues such as airplanes, cruise ships, etc.
Region 0 designates no actual region, but it is used as a shorthand for a disc meant to be playable on all players. On such a disc, the actual region coding is R1/2/3/4/5/6. In the early days, region 0 players were created that would allow any region disc to be played in them, but studios responded by adjusting regioned discs to refuse to play if the player was determined 0 (since no player should anyway).
Region code enforcement is viewed by some as a violation of WTO free trade agreements; however, no legal rulings have yet been made in this area. However, many manufacturers of DVD players now freely supply information on how to disable the region code checking, and on some recent models, it appears to be disabled by default.
HistoryDuring the early 1990s there were two high density optical storage standards in development. One was the Multimedia Compact Disc (MMCD) backed by Philips and Sony. The other was the Super Disc (SD) supported by 8 major consumer electronics giants (including Toshiba and Time-Warner). In the 1980s two incompatible video formats had been launched on the consumer market with VHS and Betamax. This slowed the uptake of this technology as many consumers chose to wait to see which format would become the most popular. To order to avoid a repeat of this, all parties agreed on the new DVD format in December, 1995. By this stage the term Digital Versatile Disk was used by some companies to reflect the fact that non-video formats of the disk would also be used.
DVD-AudioDVD-Audio is a new format to deliver high-fidelity audio content on a DVD. It offers many channels (from mono to 5.1 surround sound) at various sampling frequencies and sample sizes. Audio on a disc can be 16, 20, or 24 bit and can be at sampling rates of 44.1, 88.2, 176.4, 48, 96, or 192 kHz (The highest sampling rates of 176.4 and 192 kHz are limited to stereo only). In addition, different sampling sizes and frequencies can be used on a single disc. Audio is stored on the disc in LPCM format or is losslessly compressed with Meridian Lossless Packing. The DVD-Audio player may downmix surround sound to stereo if the listener does not have surround sound. DVD-Audio may also feature menus, still images, slideshows, and video. Also, DVD-Audio discs usually contain Dolby Digital or DTS versions of the audio (lossy compressed, usually downsampled to lower sampling sizes and frequencies) in the DVD-Video section. This is done to ensure compatibility with DVD-Video players.
The introduction of the DVD-Audio format angered many early-adopters of the DVD format. While the DVD-Audio discs do have higher fidelity, there is debate as to whether or not the difference is distinguishable to typical human ears. DVD-Audio currently forms a niche market, probably due to requiring new and rather expensive equipment. DVD-Audio is currently (as of 2003) in a format war with SACD.
Competitors and successorsThere are multiple successors being developed by two different consortiums: The Blu-Ray disc and the Advanced Optical Disk.
On November 18, 2003, the Chinese news agency Xinhua reports the final standard of the Chinese government-sponsored Enhanced Versatile Disc (EVD) and several patents around it.
On November 19, 2003 the DVD-Forum decided with eight to six votes that the Advanced Optical Disk is the HDTV successor of the DVD.