DVD

DVD-Video

DVD-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 audio of varying formats (often multi-channel formats as described below). Typical data rates for DVD movies range from 3-10 Mbit/s, and the bit rate is usually adaptive. The video resolution on NTSC discs is 720x480 and on PAL discs is 720x576. A high number of audio tracks and/or lots of extra material on the disc will often result in a lower bit rate (and image quality) for the main feature.

Related Topics:
MPEG-2 - Mbit/s - Bit rate

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The audio data on a DVD movie can be of the format PCM, DTS, MP2, or Dolby Digital (AC-3). In countries using the NTSC standard any movie should contain a sound track in (at least) either PCM or Dolby AC-3 formats, 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. The vast majority of commercial NTSC releases today employ AC-3 audio.

Related Topics:
PCM - DTS - MP2 - Dolby Digital - NTSC standard - AC-3

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Initially, in countries using the PAL standard (e.g. most of Europe) the sound of DVD was supposed to be standardized on PCM and MP2, 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. The vast majority of commercial PAL releases employ AC-3 audio by now.

Related Topics:
PAL - MP2 - Philips - December 5 - 1997 - DVD Forum

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DVDs can contain more than one channel of audio to go together with the video content. In many cases, sound tracks in more than one language track are present (for example the film's original language as well as a dubbed track in the language of the country where the disc is being sold).

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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.

Related Topics:
RCA jack - TOSLINK - S/PDIF

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Video is another issue which continues to present problems. Current players typically output analog video only, 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 keeps the three components of the video, one luminance signal and two color difference signal, as stored on the DVD itself, on fully separate wires (whereas s-video uses two wires, uniting and degrading the two color signals, and composite only one, uniting and degrading all three signals). Additionally, the connectors are further confused by using a number of different physical connectors on different player models, RCA or BNC, as well as using VGA cables in a non-standard way (VGA is normally analog RGB, not component). Even worse, there are often two sets of component outputs, one carrying interlaced video, and the other progressive. In Europe and other PAL areas, SCART connectors are typically used, which carry both composite and analog RGB interlaced video signals, as well as analog 2-channel sound on a single multiwire cable, and which offer a reasonable compromise between video quality -- which is superior to S-Video though inferior to progressive component video -- and cost. HDMI is a new connection similar to SCART, but it carries High Definition, Enhanced Definition and Standard Definition video. Along with video HDMI also supports up to 8-channel digital audio.

Related Topics:
Analog - Composite video - S-Video - Progressive video - Component video - BNC - VGA - RGB - Interlaced video - SCART - HDMI

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DVD Video may also include one or more subtitle tracks in various languages, including those made especially for the hearing impaired. They are stored as images with transparent background which are overlaid over the video during playback. Subtitles are restricted to four colors (including transparency) and thus tend to look cruder than permanent subtitles on film.

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DVD Video may contain Chapters for easy navigation (and continuation of a partially watched film). If space permits, it is also possible to include several versions (called "angles") of certain scenes, though today this feature is mostly used -- if at all -- not to show different angles of the action, but as part of internationalization to e.g. show different language versions of images containing written text, if subtitles won't do.

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A major selling point of DVD Video is that its storage capacity allows for a wide variety of extra features in addition to the feature film itself. This can include audio commentary that is timed to the film sequence, documentary features, unused footage, trivia text commentary, simple games and film shorts.

Related Topics:
Audio commentary - Documentary

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Restrictions

DVD-Video has four complementary systems designed to restrict the DVD user in various ways: Macrovision, Content Scrambling System (CSS), region codes, and disabled user operations (UOPs).

Related Topics:
Macrovision - Content Scrambling System - Region codes

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Content-scrambling system

Many 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). Usually, users need to install software provided on the DVD or downloaded from the Internet such as WinDVD to be able to view the disc in a computer system.

Related Topics:
Content-scrambling system - WinDVD

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The CSS system has caused major problems for the inclusion of DVD players in any open source operating systems, since open source player implementations are not officially given access to the decryption keys or license the patents involved in the CSS system. Proprietary software players were also difficult to find on some platforms. However, a 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 controversial U.S. Digital Millennium Copyright Act, on the grounds that such software could also be used to facilitate unauthorized copying of the data on the discs. But as US law stops at the border of the United States, the rest of the world can enjoy de-scrambling software to bypass the DVD cartel restrictions. A number of software programs have since appeared on the web to view DVDs on a number of platforms.

Related Topics:
Open source - Patent - Proprietary software - Reverse engineering - DeCSS - Digital Millennium Copyright Act - Number of software programs

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The restrictions also prevent people from copying DVDs. In the past few years a large amount of software has been created to make copies such as DVD Shrink, DVD Decrypter and ShrinkTo5.

Related Topics:
DVD Shrink - DVD Decrypter

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Region codes

Each DVD-Video disc contains one or more region codes, denoting the area of the world in which distribution and playback are intended. The commercial DVD-Video player specification dictates that a player must only play discs that contain its region code. In theory, this allows the motion picture studios to control the various aspects of a release (including content, date and price) on a region-by-region basis. In practice, many DVD players allow playback of any disc, or can be modified to do so. Entirely independent of encryption, region coding pertains to regional lockout, which originated in the video game industry.

Related Topics:
Regional lockout - Video game

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See a world map showing region codes

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European Region 2 DVDs may be sub-coded "D1" through "D4." "D1" identifies a UK-only release. "D2" and "D3" identify European DVDs that are not sold in the UK and the Republic of Ireland. "D4" identifies DVDs that are distributed throughout Europe.

Related Topics:
UK - Ireland

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Any combination of regions can be applied to a single disc. For example, a DVD designated Region 2/4 is suitable for playback in Western Europe, Oceania and any other Region 2 or Region 4 area. Often labeled "all" or "all regions," a so-called "Region 0" disc (actually coded Region 1/2/3/4/5/6) is meant to be playable worldwide.

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The term "Region 0" also describes DVD players that were designed or modified to incorporate Regions 1-6 simultaneously, thereby providing compatibility with virtually any disc, irrespective of region. This apparent solution was popular in the early days of the DVD format, but studios quickly responded by adjusting discs to refuse to play in such machines. This system is known as "Regional Coding Enhancement" or RCE.

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Nowadays, many "multi-region" DVD players defeat regional lockout and RCE by automatically identifying and matching a disc's region code and/or allowing the user to manually select a particular region. Others simply bypass the region code check entirely. Some manufacturers of DVD players now freely supply information on how to disable regional lockout, and on some recent models, it appears to be disabled by default.

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Many view region code enforcement as a violation of WTO free trade agreements; however, no legal rulings have yet been made in this area.

Related Topics:
Violation - WTO - Trade

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User operations

DVD-Video allows the disc to specify whether or not the user may perform any operation, such as selecting a menu, skipping chapters, forwarding or rewinding—essentially any function on the remote control. This is known as User Operation Prohibitions, or UOPs for short. Most DVD players respect these commands, although some can be configured to ignore them. Many grey-market players ignore UOPs.

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