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Video
DVD Introduction




DVDs are identical to CDs in size and appearance, but advances in the amount of information in the form of bits and bytes that can be recorded onto these discs has meant that full length movies can be stored on a DVD - and the picture quality is extremely good. (see the difference between CD and DVD) They are also, unlike VHS tapes, very robust, last longer, and there's no messy tape to get snagged up in video recorders. More... about DVD recorders.

DVD-Video was originally designed to meet the requirements of the movie industry, in particular for a complete movie on a single 'compact' optical disc. The use of MPEG-2 video compression has been shown to give superlative results, far better than VHS and better than Laserdisc.

DVD-Video also offers full surround sound, subtitling, a choice of display formats and user interaction for non-linear video applications.

DVD-Video players were launched in Japan in November 1996, in the USA in March 1997 and in Europe in 1998. Since then DVD-Video has grown faster than any other consumer electronics format in all these regions. Many thousands of titles and tens of millions of players are now in use around the world, with annual sales of players and discs almost doubling each year in some regions. DVD Video recorders that use recordable DVD discs are also now available to consumers, and are rapidly replacing VCRs.

The DVD-Video specification was written and is now maintained by the DVD Forum working group WG1, which comprises a number of task groups concerned with both read-only and recordable disc formats.

DVD-Video is now replacing VHS as the format of choice for pre-recorded movies, both retail and rental and disc sales now exceed VHS sales in many regions. With the introduction of recordable versions DVD-Video is now set to replace the VHS VCR for home video recording as well as playback of pre-recorded video.

DVD-Video Requirements

The Hollywood based Motion Picture Studio Advisory Committee defined the following requirements for the DVD-Video format:

  • 135 minutes on one side of a single disc (covering 99% of all movies).
  • Video resolution better than Laserdisc (LD).
  • CD quality surround sound for true home cinema listening.
  • 3 to 5 languages (audio) per title on one disc
  • 4 to 6 subtitles per title on one disc
  • Pan-scan, letterbox and widescreen formats
  • Parental lock features
  • Copy protection
  • Compatibility with existing CDs
  • Chapter division and access (like Video CD)
  • Manufacturing cost similar to current CD costs.

The Video CD format was studied, but was rejected as it could not offer the necessary combination of quality and playing time, hence the need for a new higher capacity disc format that has been realized in DVD. The above requirements have all been met in the DVD-Video specification.

DVD-Video Features

The DVD-Video specification provides the following features:

  • 133 minutes of high quality MPEG-2 encoded video with multi-channel surround sound audio.
  • The choice of widescreen, letter box and pan & scan video formats.
  • Audio in up to 8 languages
  • Subtitles for a further 32 languages
  • Menus and program chains for user interactivity
  • Up to 9 camera angles to give the user more choice
  • Digital and analogue copy protection
  • Parental control for protection of children

Most DVD-Videos also include extras that cannot be included on a VHS movie, such as biographies, director's commentary, making of the movie etc.  An increasing number include DVD-ROM content, which can range from links to relevant websites to a full game based on the movie.  The use of websites can allow the disc to be used in different ways with updated text and graphics information on the website complementing the video on the disc.

The DVD-Video specification is based on a pre-recorded DVD (DVD-ROM) with UDF Bridge file system. A DVD-Video can therefore be a DVD-5, DVD-10 or DVD-9 disc depending on the playing time required and other factors.

For overall playing times longer than 133 minutes (including additional content), the dual layer DVD-9 offers a solution.

A DVD-10 is more useful where widescreen and pan & scan versions are required on the same disc. The use of the DVD-10 format is not recommended for longer playing times, as the disc needs to be flipped to play the other side.

DVD and CD : What is the difference?
Data Storage: DVD vs. CD

DVD can store more data than CD for a few reasons:
  • Higher-density data storage
  • Less overhead, more area
  • Multi-layer storage

Higher Density Data Storage
Single-sided, single-layer DVD can store about seven times more data than CD. A large part of this increase comes from the pits and tracks being smaller on DVD.

 
Specification
CD
DVD
Track Pitch (nanometers)
1600
740
Minimum Pit Length
(single-layer DVD)
830
400
Minimum Pit Length
(double-layer DVD)
830
440

Let's get an idea of how much more data can be stored due to the physically tighter spacing of pits on a DVD. The track pitch on a DVD is 2.16 times smaller, and the minimum pit length for a single-layer DVD is 2.08 times smaller than on a CD. By multiplying these two numbers, we find that there is room for about 4.5 times as many pits on a DVD. So where does the rest of the increase come from?

Less Overhead, More Area
On a CD, there is a lot of extra information encoded on the disc to allow for error correction -- this information is really just a repetition of information that is already on the disc. The error correction scheme that a CD uses is quite old and inefficient compared to the method used on DVD. The DVD format doesn't waste as much space on error correction, enabling it to store much more real information. Another way that DVDs achieve higher capacity is by encoding data onto a slightly larger area of the disc than is done on a CD.

Multi-Layer Storage
To increase the storage capacity even more, a DVD can have up to four layers, two on each side. The laser that reads the disc can actually focus on the second layer through the first layer. Here is a list of the capacities of different forms of DVDs:

 
Format
Capacity
Approx. Movie Time
Single-sided / single-layer
4.38 GB
2 hours
Single-sided / double-layer
7.95 GB
4 hours
Double-sided / single-layer
8.75 GB
4.5 hours
Double-sided / double-layer
15.9 GB
Over 8 hours

You may be wondering why the capacity of a DVD doesn't double when you add a whole second layer to the disc. This is because when a disc is made with two layers, the pits have to be a little longer, on both layers, than when a single layer is used. This helps to avoid interference between the layers, which would cause errors when the disc is played.

What is DVD?

DVD stands for both Digital Video Disk and Digital Versatile Disk. This is because the format, although initially used as a home video medium, has a wide variety of potential applications.

A Format for Multiple Purposes:

For a long time technical pundits have predicted that the computer, television, audio equipment, etc. would converge into a common format. DVD is the fulfillment of this prediction. In addition to home video, the DVD format can be used for storing data, dramatically increasing capacity over the current CD-ROM. It will also extend the amount of music or audio stored on an Audio CD. Other uses of DVD include interactive video, games, photo, and more. DVD is truly a "versatile" format. The consumer will no longer need separate hardware to play both video and audio discs. And he can attach the DVD player to a computer to access high capacity DVD-ROM.

A Wealth of Features:

The DVD format will provide a list of features unprecedented in the history of consumer electronics. These include multiple soundtracks, subtitles, aspect formats, MPAA versions and film releases on the same disc.

Backward Compatibility to Current Formats:

DVD also protects the consumer's current investment in Audio CD, CD-ROM CDR, etc. The DVD players will be able to play back these existing formats.

Competitive Costs:

DVD players are priced in the $40 to $600 range, depending on features. Discs are priced from $7 to $30 for feature films. The costs of replicating DVDs are significantly less than for VHS tape or laser discs. The costs of mastering, however, are much higher than for VHS tape, and somewhat more than laser discs. This skews the economics of DVD in favor of high volume, low priced DVD content. Replication of DVDs is faster than VHS Tape. Under operation, a DVD replicator can produce one disc every six seconds. Once a master has been encoded and cut, low volume production runs can be easily accommodated. In summary, the DVD format is priced at a level very attractive to consumers.

Picture and Sound Quality:

The quality of DVD is close to source, D1, material; 720 pixels per horizontal line vs. 320 pixels for VHS Tape. HDTV versions will have even greater resolution. Because DVD is digital, the NTSC artifacts of analog formats are completely eliminated. DVD delivers outstanding picture clarity and color sharpness. The DVD format provides multiple CD quality audio with Dolby Digital, discrete 5.1 surround sound, to recreate the theater experience in your own home.

Technical Specifications

Size:

The DVD disc is 4.8" in diameter (12cm), the same size as a compact disc (CD). A 3" (8cm) disc is also available.

Capacity:

Currently there have been seven DVD formats, with various capacities, proposed. Those which have been announced are:

  • SD5 4.7 GB, play only, single sided, single layered
  • SD9 8.5 GB, play only, single sided, dual layered
  • SD10 9.4 GB, play only, dual sided, single layered (2 SD5s)
  • SD18 17 GB, play only, dual sided, dual layered
  • SD-R 7.6 GB, Write once, dual sided, single layered (WORM)
  • SD-RAM 5.2 GB, Read/Write, dual sided, single layered (Erasable)
  • SD-HDTV 20+ GB, play only using blue laser for higher disc capacity

The capacity of DVD will allow most feature films to be recorded on single sided, single layer of a disc. This eliminates the need to flip or change discs in the middle of a film. Some of the movies that do not fit on a single sided, single layer disc will require you to flip the disk over, like you do with all laser disc. As more studios are putting movies that exceed the 133 minuets on dual layer disc using RSDL (Reverse Spiral Dual Layer) technology, a movie will be able to play seamlessly without requiring to flip the disc over.

Regional Coding

In the video studios' effort to prevent exporting, discs manufactured in one region will only play on players manufactured in that same region.

  • Region 1: The U.S., its territories and Canada
  • Region 2: Europe, Japan, the Middle East, Egypt, South Africa, Greenland
  • Region 3: Taiwan, Korea, the Philippines, Indonesia
  • Region 4: Mexico, South America, Australia, New Zealand
  • Region 5: Russia, Eastern Europe, India, most of Africa
  • Region 6: China

The Region Code is specified on the back of the DVD package, either with a Regional Coding logo of a globe with the region number superimposed on it or spelled out on the MGM discs: "This disc has been encoded for region 1: The United States, U.S. territories and Canada." Some discs have no regional coding--Lumivision discs are labeled "Available worldwide," but some other studios have not specified the Region Code one way or another.

 

Audio Specifications:

AC-3, discrete digital 5.1 channel Surround Sound:

CD quality sound with AC-3 surround stereo has been adopted for the DVD format. Europe has adopted the AC-3 sound also. It is hoped, however, that a single format will be adopted worldwide, eliminating the need to produce two different soundtracks.

Multiple Sound Tracks:

DVD can include up to eight separate AC-3 soundtracks to accommodate different languages or other audio nuances. This allows multiple audio versions of a film to be delivered on a single disc. Although most of the movies only have one to three different language tracks, it depends on the language within the region codes, for example region 1 will have an English, French, and Spanish audio tracks. With extra room for audio tracks some studios also have put audio commentaries with the movies, this allows you to watch the movie while the director, talks about the movie. 

Multiple Subtitles:

Up to 32 subtitle tracks can be stored on a single DVD. A viewer can choose the subtitle to be displayed or suppress subtitles altogether. Subtitles are bit-mapped so that non-ASCII characters, such as Asian languages, can be accommodated. This will also allow overlays of graphics, such as a grid or play diagrams, on the screen.

Features of Dolby AC-3 vs. Pro-Logic:

While Dolby Labs developed both formats, Dolby Digital 5.1 sound is stored on six separate channels. This is known as discrete 5.1 sound. There are five full range channels for front (left, center and right) and rear (left and right) speakers, plus a low frequency "woofer" channel. These signals are amplified separately and sent to the speakers. The channels are never mixed.

With Dolby Pro-Logic four channels (left, center, right and rear) are matrixed into two standard stereo channels. The two rear speakers receive a monaural, limited frequency range signal, these are decoded upon playback into the four channels. With this format there are some blending of the channels, resulting in a loss of directional effects and a less dynamic recreation of the soundtrack.

Dolby Digital 5.1 is the true state of the art in creating the audio ambiance of a movie theater in your home. Sounds can be placed and moved anywhere in relationship to the listener; providing full 360 degree audio.

 

Video Specifications

Aspect Ratio Support:

DVD format can contain 16x9, Letterbox, and Pan & Scan formats on the same disk.  Discs list the aspect ratios of the Letterboxed transfers, whether 1.85:1 or 2.35:1. If the disc contains a Pan & Scan transfer, that is also specified.

Some movies contain both Widescreen and Pan & Scan versions on the same disc, they have the Letterbox version on the A Side and the Pan & Scan version on the B Side. Some discs feature  the "dual-layer" format, where two sides worth of programming can be read by the DVD player from one side of the disc. When these discs are started, the viewer is first given an on-screen option to choose the widescreen or full-screen version.

Because of the large quantities of data stored on the disc for some of the longer films, a few discs contain only one version of the film, either Letterbox or Pan & Scan. Very few films will require using both sides; most films up to approximately 2 hours 15 minutes or more will fit on one side of a DVD. Unlike laserdisc, which has a strict time limit per side of 30 minutes for CAV and 60 minutes for CLV, DVD discs are limited by the amount of data they can hold. 

On DVD, 120 minutes of fast action, spinning cameras and constantly changing visuals take up more disc space than 120 minutes of stationary cameras and very little on-screen movement. Studios are now starting to put movies requiring two sides on one side using dual-layer discs, and that the DVD player will be able to switch from one layer to the other automatically and with little or no visible break.

Enhanced for 16x9 widescreen TV's

DVD is the first video format (apart from a few Japanese laserdiscs) to take full advantage of 16 x 9 TV capabilities, with these "enhanced for 16 x 9" DVDs and the TV's special circuitry squeezing more "lines of resolution" onto the screen than a regular 4 x 3 TV set can.

A 4 x 3 aspect ratio TV set picture is made up of approximately 480 horizontal lines of resolution from the top of the screen to the bottom. A laserdisc or video tape letterboxed at 2.35:1 uses only around 270 of those lines of resolution to display the picture; the other 210 lines make up the black bars you see at the top and bottom of the screen.

On an "enhanced for 16 x 9" DVD disc (also known as an "anamorphic" DVD), that same 2.35:1 letterboxed image is stretched vertically to use all 480 lines of resolution. (If you were to look at that image without any further processing, all of the actors would appear unnaturally tall and thin.) Then, the special circuitry in the 16x9 TV set squeezes those 480 lines of picture back down to the proper size. In effect, a picture that would be made up of 270 lines of resolution on a regular 4 x 3 TV set is made up of a full 480 tightly-spaced lines on a 16 x 9 set, resulting in finer detail than regular TVs can display.  

MPAA Rating Control:

A single DVD disc can contain multiple versions of a movie with different MPAA ratings. This allows a viewer to select the version of the film he or she prefers. For example, a viewer could choose the "R" or "PG-13" version of a particular film. This feature also allows parental lockout, so that a child or other person, without the correct access code, could not view film versions above a certain MPAA rating. Furthermore, this feature allows certain countries to mandate that players sold in that country be outfitted with a chip which prohibits viewing of films above a certain MPAA rating. This eliminates the need to produce different versions of a film with different MPAA ratings for countries with content restrictions. When played, certain scenes will be skipped or alternative scenes shown according to the MPAA rating chosen. This "editing" occurs seamlessly without interruption of the playback. However no studio has yet implemented this feature, but Columbia Tri-Star do offer the parental lockout on some titles.

Multiple Film Versions:

DVD allows multiple versions of a film to be recorded on a single disc. For example a disc could contain both the theatrical and "director's cut" of a movie. The user could then choose which version of the film to watch. When played, certain scenes will be skipped or alternative scenes shown according to the film version chosen. This "editing" occurs seamlessly without interruption of the playback. However there are many director’s cut titles on DVD, no title has the option of choosing one or the other.

 

Miscellaneous

Audio-CD and CD-ROM Compatibility:

Audio DVD. This audio format with higher fidelity and capacity than the current audio CD format is available. Current audio CDs can be played on DVD players. DVD-ROM will provide a more than ten-fold increase in capacity over current CD-ROM discs. DVD players playback current CD discs.

Costs:

DVD players are ranging from $35 to over $400 depending on the features. DVD disc prices range from $5 to $25 for most feature films. These prices make DVD very competitive to other video formats.

Other DVD Uses:

DVD-Interactive will allow games to be distributed on DVD format. The higher capacity will allow better graphics and more sophisticated games to be designed. DVD-Photo will accommodate stock photographs to be distributed with greater resolution and capacity then current CD-ROM formats. This may allow the migration from film to electronic storage of photographs.

 

 

The History of DVD

DVD developments started in 1994 and the format was launched in 1996.  Since then new formats and revisions have appeared.

Year

Events

1994

Hollywood ad hoc committee defined features for movies on a 'compact disc'.

1995

Philips/Sony announced and demonstrate MMCD.
Toshiba & Warner announce and demonstrate SD.
Agreement is reached on a single standard format called DVD that combines the best of MMCD and SD.

1996

 

DVD-ROM and DVD-Video specifications version 1.0 published.
Digital copy protection scheme (CSS) agreed.
First DVD-Video players sold in Tokyo (Nov).

1997

Launch of DVD in USA (Aug). DVD-R release followed.
DVD Consortium becomes DVD Forum, expands membership and holds first General DVD Forum Meeting with 120 members

1998

DVD-Video version 1.1 and DVD-ROM version 1.01 specifications released.
DVD Forum adopts DVD-RW.
DVD Forum announces 7 new members of DVD steering committee making 17 in all.
DVD Forum publishes DVD-Audio (version 0.9) specification 
Full launch of DVD in Europe
1m DVD-Video players sold in USA
4.7 GB DVD-R and DVD-RAM version 1.9 specifications released

1999

DVD-Audio (1.0), DVD-Video Recording (0.9 & 1.0), DVD-RW (0.9) and DVD-RAM (2.0) specifications published. 

2000

CPPM copy protection for DVD-Audio agreed
DVD-Audio players launched in USA (Jul)
First DVD-Audio discs in USA (Nov)
DVD-RW Part 2 (1.0), DVD-R for Authoring (2.0), DVD-R for General (2.0) and DVD Stream Recording (0.9) specifications published.

2001

DVD-Audio players & discs available
DVD Video Recorders launched in Europe etc
DVD-Multi (1.0), DVD Stream Recording (1.0), DVD-Audio (1.2) and DVD-Video Recording (1.1) specifications published.
DVD+RW introduced.
Guidelines for IEEE 1394 transmission for DVD-Video/Audio issued.

2002

WG-11 created to study future blue laser format
DVD-Audio recording specification ver 0.9 issued. DVD+R introduced.
Hybrid DVD-Audio format considered by DVD Forum

2003

DVD Forum rejects hybrid DVD-Audio format
DVD Forum releases iDVD specifications to provide more interactivity for DVD-Video.

2004

DVD High-Definition formats Blu-ray and HD-DVD compete for eventual market dominance.
DVD Universal players available which can play DVD Video, DVD Audio, SACD, CD and more.
DVD recorders prices fall. DVD blank media DVD-R, DVD+R, DVD-RW and DVD+RW prices fall.
 


Learn about the various video formats:
Video formats
Learn about DVD features:
features

How do I record on a DVD recorder?

DVD Player Audio setup

How do I connect my DVD player?