DVD-Video

DVD-Video

File:Dvd-video-logo.svg DVD-Video format logo
Media type	Optical disc
Capacity	up to 8.5 GB
Standard	DVD Books, Part 3, DVD-Video Book (Book B), DVD Video Recording Book
Developed by	DVD Forum
Usage	Video storage
Extended from	DVD

DVD-Video is a consumer video format used to store digital video on DVD discs, and is currently the dominant consumer video format in North America, Europe, and Australia. Discs using the DVD-Video specification require a DVD drive and a 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). Typically, data rate for DVD movies range from 3 Mbit/s to 9.5 Mbit/s, and the bit rate is usually adaptive.

The DVD-Video specification was created by DVD Forum and can be obtained from DVD Format/Logo Licensing Corporation for a fee of $5000. The specification is not publicly available, because every subscriber must sign a non-disclosure agreement. Certain information in the DVD Book is proprietary and confidential.

Frame size and frame rate

To record moving pictures DVD-Video utilizes either MPEG-2 compression at up to 9.8 Mbit/s (9800 kbit/s) or MPEG-1 compression at up to 1.856 Mbit/s (1856 kbit/s).

The following formats are allowed for MPEG-2 video:

• At 25 frame/s, interlaced (commonly used in regions with 50 Hz image scanning frequency):

720 × 576 pixels (same resolution as D-1)

704 × 576 pixels

352 × 576 pixels (same as the China Video Disc standard)

• At 29.97, interlaced (commonly used in regions with 60 Hz image scanning frequency):

720 × 480 pixels (same resolution as D-1)

704 × 480 pixels

352 × 480 pixels (same as the China Video Disc standard)

The following formats are allowed for MPEG-1 video:

• 352 × 288 pixels at 25 frame/s, progressive (Same as the VCD Standard)
• 352 × 240 pixels at 29.97 frame/s, progressive (Same as the VCD Standard)

All resolutions support video with 4:3 frame aspect ratio. Only full D1 resolutions support widescreen (16:9) video.

MPEG-1 formats do not support interlaced video. MPEG-2 formats support both interlaced and progressive-scan content, with the latter being encoded within interlaced stream using pulldown.

MPEG-2 encoder can add flags in video stream to indicate scanning type, field order and field repeating. A DVD player uses these flags to convert progressive content into interlaced video suitable for interlaced TV sets. These flags also help reproducing progressive content on progressive-scan television sets.

Audio data

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. DTS audio is optional for all players, as DTS was not part of the initial draft standard and was added later; thus, many early players are unable to play DTS audio tracks. The vast majority of commercial DVD-Video releases today employ AC-3 audio. 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 Linear PCM, 2 to 6 channels, up to 6144 kbit/s. N.B. 16-bit 48 kHz 8 channel PCM is allowed by the DVD-Video specification but is not well-supported by authoring applications or players.
• 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—DTS 5.1, AC-3 2.0 etc.—as well as for commentary and audio tracks in different languages.

Data rate

DVD-Video discs have a raw bitrate of 11.08 Mbit/s, with a 1.0 Mbit/s overhead, leaving a payload bitrate of 10.08 Mbit/s. Of this, up to 3.36 Mbit/s can be used for subtitles and a maximum of 9.80 Mbit/s can be split amongst audio and video. In the case of multiple angles the data is stored interleaved, and so there's a bitrate penalty leading to a max bitrate of 8 Mbit/s per angle to compensate for additional seek time. This limit is not cumulative, so each additional angle can still have up to 8 Mbit/s of bitrate available.

Professionally encoded videos average a bitrate of 4-5 Mbit/s with a maximum of 7–8 Mbit/s in high-action scenes. This is typically done to allow greater compatibility amongst players, and to help prevent buffer underruns in the case of dirty or scratched discs.

Columbia TriStar Home Entertainment has created a line of DVDs (dubbed "Superbit") aiming to maximize picture quality by eliminating multiple languages, angles, and audio tracks. This allows average bitrates closer to 6 Mbit/s.

Other features

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) that DVD players use to navigate the disc.

The maximum chapters allowed per title is 99 and the maximum titles allowed per DVD is 99.

Container

Main article: VOB

Video, audio and subtitle streams are multiplexed and stored on a DVD-Video disc in the VOB container format (Video Object). VOB is based on the MPEG program stream format, but with additional limitations and specifications in the private streams. The MPEG program stream has provisions for non-standard data (as AC-3, DTS, LPCM or subtitles used in VOB files) in the form of so-called private streams. VOB files are a very strict subset of the MPEG program stream standard. While all VOB files are MPEG program streams, not all MPEG program streams comply with the definition for a VOB file.

DVD Recorders can use DVD-VR or DVD+VR format instead of DVD-Video. DVD-VR format store multiplexed audiovisual content in VRO containers. VRO file is an equivalent to a collection of DVD-Video VOB files. Fragmented VRO files are not widely supported by hardware or software players and video editing software. DVD+VR standard defines a logical format for DVD-Video compliant recording on optical discs and is commonly used on DVD+R/RW media.

See also: DVD-VR and DVD+VR

Subtitles

DVD Video may also include up to 32 subtitle or subpicture tracks. Subtitles are usually intended as a visual help for the deaf and hearing impaired and for translating dialogs.

Subtitles can serve other purposes as well. For example, in the DVD release of Thirteen Days one of the subtitle tracks includes history notes, giving additional information timed to the events depicted in the film. In the release of For All Mankind subtitles display names of the NASA missions and names of the people shown on the screen.

Subtitles are stored as bitmap images and therefore can contain messages in any language. Subtitles are restricted to four colors, including transparent "color", and thus tend to look cruder than permanent subtitles on film. Transparency allows laying subtitles over the video during playback. The subtitle tracks are contained within the VOB file of the DVD.

DVD Video may also contain closed captioning material which can only be viewed on a television set with a decoder.

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, for example, show different language versions of images containing written text, if subtitles will not do (e.g., 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.

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, deleted scenes, photo galleries, storyboards, isolated music scores, trivia text commentary, simple games, film shorts, TV spots, radio spots and most commonly theatrical trailers and teaser trailers, the extra features can also can include the making of the film.

The extra (or bonus) features are often popular with the audience as they can add extra depth and understanding to the film. Games, bloopers and galleries can provide extra entertainment, especially for younger ages. Deleted scenes and alternative endings further the imagination and allow the audience to form a personal judgement on whether the best scenes were selected.

Other extras that can be included on DVDs are motion menus, still pictures, up to 32 selectable subtitles, seamless branching for multiple storylines, up to 9 camera angles, and DVD-ROM / data files that can be accessed on a computer equipped with a DVD-ROM capable drive.

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). There are also anti-ripping techniques intended to foil ripping software.

Content Scramble System

Many DVD-Video titles use Content Scramble 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 MPlayer, PowerDVD, VLC or WinDVD to be able to view the disc in a computer system.

CSS does not make it more difficult to copy the digital content, nor possible to distinguish between legal and illegal copies of a work, but it does restrict the playback software that may be used.

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 to the patents involved in 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 (DMCA), on the grounds that such software could also be used to facilitate unauthorized copying of the data on the discs. The Videolan team, however, went on to make the libdvdcss library. Unlike DeCSS, libdvdcss can access a CSS-encypted DVD without the need of a cracked key, thus enabling playback of such discs on opensource players without legal restrains.

The DMCA currently affects only the United States, however many other countries are signatories to the similar WIPO Treaty. In some countries it is not illegal to 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 anti-ripping, as well as U.S. and non-U.S. copyright law, may be used to prevent making unauthorized copies of DVDs. CSS decrypting software, or ripping software, such as DVD Decrypter, AnyDVD, Handbrake, AVS Video Converter and DVD Shrink allows a disc to be copied to hard disk unscrambled. Some DeCSS applications also remove Macrovision, region codes, and disabled user operations (UOPs).

Anti-ripping

After DeCSS ripping software became available, companies developed techniques to introduce errors in DVD-Video discs that don't normally affect playback and navigation of a disc, but can cause problems in software that attempts to copy the entire disc. These approaches, which are not part of the official DVD-Video specification, include Sony ARccOS, Macrovision RipGuard, X-protect, ProtectDisc SecureBurn, Anaho , Fortium, and others. All of these methods have been circumvented (as might have been expected, since all standard DVD players naturally circumvent them to play and navigate the discs normally.) Riplock is a feature that reduces drive noise during playback but inadvertently reduces ripping speed.

Disabled user operations

Main article: User operation prohibition

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 skipping or fast-forwarding through a copyright message or an advertisement at the beginning of a disc). However, grey market players ignore UOPs and some DVD "re-authoring" software packages allow the user to produce a copy without these restrictions. The legality of these activities varies by jurisdiction and is the subject of debate. (See fair use.)

Region codes

Main article: DVD region code

DVD region codes across the world

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 delayed cinema releases from country to country. For example, the British movie 28 Days Later was released on DVD in Europe several months prior to the film's release in North American movie theaters. Regional coding kept the European DVD unplayable for most North American consumers, thereby ensuring that ticket sales would be relatively unaffected.

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. 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 (at the very least, in black and white), 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 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.

The CSS license prohibits manufacturing of DVD players that are not set to a single region by default. While the same license prohibits manufacturers from including prominent interfaces to change the region setting it does not clearly prevent them from including "hidden" menus that enable the player's region to be changed; as such, many high-end models in the U.S. include password-protected 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.

Programming interface

A virtual machine implemented by the DVD player runs bytecode contained on the DVD. This is used to control playback and display special effects on the menus. The instruction set is called the Virtual Machine (VM) DVD command set. There are 16 general parameter registers (GPRM) to hold temporary values and 24 system parameters (SPRM). As a result of a moderately flexible programming interface, DVD players can be used to play games, such as the DVD re-release of Dragon's Lair, along with more sophisticated and advanced games such as Scene It, all of which can be run on standard DVD players.

Players and recorders

Main articles: DVD player and DVD recorder

Modern DVD recorders often support additional formats, including DVD+/-R/RW, CD-R/RW, MP3, WMA, SVCD, JPEG, PNG, SVG, KAR and MPEG-4 (DivX/Xvid). Some also include USB ports or flash memory readers. Player prices range from as low as US$20 (GB£10) to as high as US$2,700 (GB£1,350).

DVD drives for computers usually come with one of two kinds of Regional Playback Control (RPC), either RPC-1 or RPC-2. This is used to enforce the publisher's restrictions on what regions of the world the DVD can be played. (See Regional lockout and DVD region codes.) While Open source software DVD players allow everything, commercial ones (both standalone models and software players) come further encumbered with restrictions forbidding the viewer from skipping (or in some cases fast-forwarding) certain content such as copyright warnings or advertisements. (See User operation prohibition.)

Video game systems with DVD-Video playback functionality are PlayStation 2, PlayStation 3, Xbox (additional remote required), Xbox 360, Panasonic Q, and Wii (with an unsupported hack).

Competitors and successors

In April 2000, Sonic Solutions and Ravisent announced hDVD, an HDTV extension to DVD. However hDVD failed to gain much popularity.

On November 18, 2003, the Chinese news agency Xinhua reported the final standard of the Chinese government-sponsored Enhanced Versatile Disc (EVD) which is another extension of standard DVD. Shortly thereafter the development of the format was halted by a licensing dispute between Chinese companies and On2 Technologies, but on December 6, 2006, 20 Chinese electronic firms unveiled 54 prototype EVD players and announced their intention for the format to completely replace DVDs in China by 2008. However, due to a lack of sales, support for EVD has recently been dropped by the Xinhua Bookstore in Wuhan, which was a major supporter of the format.

Blu-ray Disc & HD DVD

See also: High definition optical disc format war

2006 saw the introduction of two competing high-definition optical-disc formats, HD DVD and Blu-ray. The HD DVD format, promoted by Toshiba, had the backing by the DVD Forum, which voted to make it the official successor to DVD. Opposing HD DVD was the Blu-ray format, led by the Blu-ray Disc Association, which shares many of the same members.

Despite HD DVD's slight market lead and earlier introduction to the retail market (March 2006 vs June 2006), both formats engaged in a brief format war. Industry analysts likened the situation to the VHS/Betamax format war of the 1980s. But this time, consumer awareness of either high-definition format was severely limited, with the end result that most consumers avoided either format, already content with DVD. Toshiba capitulated in February 2008, citing low demand for HD DVD and the faster growth of Blu-ray, among other reasons. Toshiba ended production of their HD DVD players and discontinued promotion of the format, while the HD DVD movie release schedule concluded by June 2008.

As of February 2009, Blu-ray disc is the de-facto high-definition optical-disc format. However, sales-figures suggest DVD is in no immediate danger of disappearing. Until households acquire high-definition capable displays, they have no reason to switch to Blu-Ray (Other than more data capacity and less disc scratching), while households which are already equipped with HD-capable displays overwhelmingly have access to competing sources of HD-video, from traditional subscription-based cable/satellite TV, to the fast growing market of internet-hosted video-download services.

It should be noted, however, that all standard DVDs will play on existing Blu-ray players, making the switch to Blu-ray much easier than the switch from VHS to DVD was 10 years ago. And a growing number of hardware vendors are enhancing their Blu-ray players with internet-connectivity for subscription-based video downloads.

See also

• Blu-ray Disc
• HD DVD
• DVD Video Recording Mode, DVD-VR, DVD+VR
• Format war
• List of video players (software)
• Jon Lech Johansen, author of DeCSS
• Superbit
• Video Object

External links

• DVD-Video information including virtual machine instruction set information.
• Unofficial DVD Specifications Guide (Commercial site.) Includes information about the virtual machine.