DVD-Video
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DVD-Video discs require a DVD-drive and an MPEG-2 decoder (e.g. 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.
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[edit] Visual data
[edit] Resolution
The typical video resolution for an NTSC disc is 720 × 480, while a PAL disc is 720 × 576. The specifications for video files on a DVD can be any of the following:
- PAL:
- 720 × 576 pixels MPEG-2 (Called full D1)
- 704 × 576 pixels MPEG-2
- 352 × 576 pixels MPEG-2 (Called Half-D1, same as the China Video Disc standard)
- 352 × 288 pixels MPEG-2
- 352 × 288 pixels MPEG-1 (Same as the VCD Standard)
- NTSC:
- 720 × 480 pixels MPEG-2 (Called full D1)
- 704 × 480 pixels MPEG-2
- 352 × 480 pixels MPEG-2 (Called Half-D1, same as the China Video Disc standard)
- 352 × 240 pixels MPEG-2
- 352 × 240 pixels MPEG-1 (Same as the VCD Standard)
[edit] Frame rate and other requirements
All MPEG video must be 25 frames per second on PAL DVDs. On NTSC DVDs MPEG-2 video can be either 29.97 frames per second or 23.976 frames per second, while MPEG-1 video can only be 29.97 frames per second. Interlacing is only supported for MPEG-2 video on both PAL and NTSC DVDs. 16:9 aspect ratio anamorphic video is only supported at 720x576/480, and all resolutions support 4:3 aspect ratio video.
A high number of audio tracks or a large amount of extra material on the disc will often result in a lower bit rate (and image quality) for the main feature. The total bitrate including video, audio and subtitles can be a maximum of 10.08 Mbit/s (10080 kbit/s).
Some DVD-hardware or software players may play discs whose MPEG files do not conform to the above standards; commonly this is used to support DVD discs authored with formats such as VCD and SVCD. While VCD and CVD video is supported by the DVD standard, neither SVCD video nor VCD, CVD, or SVCD audio is compatible with the DVD standard.
Some hardware players will also play DVD-ROMs or CD-ROMs containing "raw" .mpg MPEG video files; these are "unauthored" and lack the file and header structure that defines DVD-Video. Standard DVD-Video files contain extra information (such as the number of video tracks, chapters and links to extra features) which DVD players use to navigate the disc.
[edit] Audio data
[edit] Audio bitrate
The audio data on a DVD movie can be PCM, DTS, MPEG-1 Audio Layer II (MP2), or Dolby Digital (AC-3) format. In countries using the PAL system standard DVD-Video releases must contain at least one audio track using the PCM, MP2, or AC-3 format, and all standard PAL players must support all three of these formats. A similar standard exists in countries using the NTSC system, though with no requirement mandating the use of or support for the MP2 format. The vast majority of commercial DVD-Video releases today employ AC-3 audio.[citation needed] The official allowed formats for the audio tracks on a DVD Video are:
- PCM: 48 kHz or 96 kHz sampling rate, 16 bit or 24 bit L-PCM, 2 to 6 channels, up to 6144 kbit/s
- AC-3: 48 kHz sampling rate, 1 to 5.1 (6) channels, up to 448 kbit/s
- DTS: 48 kHz or 96 kHz sampling rate, 2 to 6.1 channels, Half Rate (768 kbit/s) or Full Rate (1536 kbit/s)
- MP2: 48 kHz sampling rate, 1 to 7.1 channels, up to 912 kbit/s
DVDs can contain more than one channel of audio to go together with the video content, supporting a maximum of 8 simultaneous audio tracks per video. This is most commonly used for different audio formats -- 5.1 DTS, 2.0 AC3, etc. -- as well as for commentary and audio tracks in different languages.
[edit] Playback Issues
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 physical connection is typically RCA connectors or TOSLINK, which transmits a S/PDIF stream carrying either uncompressed digital audio (PCM) or the original compressed audio data (Dolby Digital (AC-3), DTS, MPEG audio) to be decoded by the audio equipment.
Video is another issue which continues to most 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, to carry a 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). 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—a different, incompatible form of component video). Even worse, there are often two sets of component outputs, one carrying interlaced video, and the other progressive. In Europe (but not most other PAL areas), SCART connectors are typically used, which can carry composite, Y/C (S-Video), and/or analog RGB interlaced video signals (RGB can be progressive, but not all DVD players and displays support this mode), as well as analog two-channel sound on a single convenient multiwire cable. The analog RGB component signal offers video quality which is superior to S-Video and identical to YPbPr component video. However, analog RGB and S-Video signals can not be carried simultaneously, due to each using the same pins for different uses, and displays often must be manually configured as to the input signal, since no switching mode exists for S-Video. (A switching mode does exist to indicate whether composite or RGB is being used.) Some DVD players and set-top boxes offer YPbPr component video signals over the wires in the SCART connector intended for RGB, though this violates the official specification and manual configuration is again necessary. (Hypothetically, unlike RGB component, YPbPr component signals and S-Video Y/C signals could both be sent over the wire simultaneously, since they share the luminance (Y) component.) HDMI is a new digital connection similar to DVI; it carries High Definition, Enhanced Definition and Standard Definition video. Along with video HDMI also supports up to eight-channel digital audio. Some HDMI-equipped DVD players can upconvert the video to higher definition formats such as 720p and, more rarely, 1080p.
[edit] Other features
[edit] Subtitles
DVD Video may also include up to 32 subtitle or subpicture tracks in various languages, including those made especially for the deaf and hearing impaired. They are stored as bitmap images with transparent background and are shown over the video during playback. The subtitle track is contained within the VOB file of the DVD. Subtitles are restricted to four colors (including transparency) and thus tend to look cruder than permanent subtitles on film.
[edit] Chapters
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 will not do (eg: the Queen's spell book in Snow White, and the scrolling text in the openings of the Star Wars films). Multiple angles have found a niche in markets such as yoga and erotica.
[edit] Extra features
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.
Other extras that can be included on DVDs (extra to the main audio/visual programme) are motion menus, still pictures, up to 32 selectable subtitles, seamless branching for multiple storylines, 9 camera angles. And also additional DVD-ROM / data files that only can be read by computer DVD drives.
[edit] Restrictions
DVD-Video has four complementary systems designed to restrict the DVD user in various ways: Macrovision, Content Scramble System (CSS), region codes, and disabled user operations (UOPs).
[edit] Content-scrambling system
Many DVD-Video titles use content-scrambling system (CSS) encryption, which is intended to discourage people from copying the disc. Usually, users need to install software provided on the DVD or downloaded from the Internet such as WinDVD, PowerDVD, MPlayer, or VLC to be able to view the disc in a computer system.
Without descrambling first, any digital copy of the disc will be ruined and unplayable everywhere, including computers.
The CSS 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. 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.
These laws currently affect only the United States; most other countries can use de-scrambling software to bypass the DVD restrictions. A number of software programs have since appeared on the Web to view DVDs on a number of different platforms.
Other measures such as RipGuard, as well as US and non-US copyright law, may be used to prevent making unauthorized copies of DVDs. CSS decrypting software (such as DVD Decrypter, AnyDVD, and DVD Shrink) allows a disc to be copied to hard disk unscrambled and (as an extra feature) region-specific DVD to be copied as an all-region DVD. It also removes Macrovision, CSS, region codes, and disabled user operations (UOPs).
[edit] Disabled 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 Prohibited User Operations (UOPs or PUOs). Most DVD players respect these commands (e.g. by preventing fast-forwarding through a copyright message or an advertisement at the beginning of a disc), although some can be configured to ignore them, particularly open-source player software.
Many grey market players ignore UOPs. Many popular DVD "reauthoring" software packages allow the user to strip out UOPs, and burn a new copy without the restrictions. While this may be illegal in some countries,[citation needed] it is commonly argued in online forums that, having legally purchased the DVD and its content, users are ethically entitled to view 'their' content the way they prefer. See the fair use provision. Many feel that being forced to watch UOP-protected content, and having functions on their playback equipment disabled, is an unfair imposition by the distributor, particularly due to the fact that UOP-protected content is almost inevitably commercial content (previews and/or advertising of other films or products), meaning that they are forced to view commercials on what they have purchased. Furthermore, ironically a greater percentage of those who do not pirate DVDs are likely to see the UOP controlled anti-piracy warnings than those who do, as the aforementioned ability of authoring software to strip such restrictions ensures that pirated DVDs need not place restrictions on, or even display, such messages.
[edit] Region codes
Each DVD-Video disc contains one or more region codes, denoting the area[s] of the world in which distribution and playback are intended. The commercial DVD 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, or ensure the success of "staggered" or late theatrical releases from country to country. For example, the movie 28 Days Later was released on DVD in Europe several months prior to the film's theatrical release in North America. Regional coding kept the European DVD unplayable for most North American consumers, thereby ensuring that ticket sales would be relatively unaffected by the late theatrical release. To many, this is no more than an objectionable barrier to trade. As a result many websites offer methods with which consumers can by-pass such restrictions.
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.
From a worldwide perspective regional coding may be seen as a failure.<ref>news.bbc.co.uk – Border controls crumble in DVD land</ref> A huge percentage of players outside of North America can be easily modified (and are even sold pre-modified by mainstream stores such as Amazon.co.uk) to ignore the regional codes on a disc. This, coupled with the fact that almost all televisions in Europe and Australasia are capable of displaying NTSC video, means that consumers in these regions have a huge choice of discs. Contrary to popular belief, this practice is not illegal and in some countries that strongly support free trade (New Zealand is one prominent example) it is encouraged.
A normal DVD player can only play region-coded discs designated for the player's own particular region. However, a code-free or region-free DVD player is capable of playing DVD discs from any of the six regions around the world.
Laws in the United States specifically prohibit the domestic sale of DVD players which are not set to Region 1 by default. While the same laws prohibit manufacturers from including prominent interfaces to change the region setting they do not prevent them from including "hidden" menus which enable the player's region to be changed; as such, many high-end models include passworded or otherwise hidden methods to enable multi-region playback. Conversely in the UK and Ireland many cheap DVD players are multi-region while more expensive systems, including the majority of home cinema systems, are preset to play only region 2 discs.
[edit] Menu programming interface
DVD players use special programming code to display special effects on the menus. It is unclear what programming language is used for this operation. However, some speculate that it may use machine language. As a result of a moderately flexible programming interface, educational DVD player games have been developed along with advanced trivia games such as Scene It; and even sophisticated games which use standard DVD players. Along with that, some console emulators may be released on DVD player images soon.
[edit] See also
[edit] References
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