DVD Format
This is an introduction to DVD Video, and explains the different types of disc, the advantages DVD has over other formats such as VHS video, and details the new features that the DVD format has made possible.



The DVD Video format offers many more features when compared to VHS and Laserdisc. DVD is essentially a digital disc the same size as a standard CD, but has a slightly different surface on which information is recorded and retrieved. The surface of the disc contains digital information in the form of microscopic pits that are interpreted by a laser pickup as a digital signal. Because there is no physical contact between the player and the surface of the disc, there is little possibility damaging the disc when in use. Only physical damage such as scratches causes the information to be harmed.

A standard single sided, single layered DVD-Video disc can hold 4.7 gigabytes of information (2 hours of video and digital surround sound), which is seven times more digital information than a normal CD. This has been made possible by reducing the size of the pits on the disc surface by about one half, and by using the MPEG2 data compression technology to reduce the size of the original information by 40 times prior to encoding onto the disc. The same compression technology is used by a DVD player when reading a disc to expand the information into a usable signal. DVD video has a picture resolution of 500 horizontal lines, giving it a sharp, high resolution appearance superior to VHS video (240 lines) and even Laserdisc (400 lines).  


The DVD Disc types:

Single Layer, Single Side. 133 Mins. The Basic and commonly used type.
Dual Layer, Single Side. 240 Mins. Will be the standard DVD format.
Single Layer, Two Sided. 266 Mins. These 'Flippers' are being phased out.
Side1 - Single Layer, Side2 - Dual Layer. DVD-9 plus DVD-9. 373 Mins.
Dual Layer DVD-9 on both sides. 480 Mins.


DVD discs are available with all the sound and picture information of a single movie recorded on a single side of the disc. Where a recording is too long to fit onto a single side, it can be recorded onto a dual-layer disc, making flipping the disc over half way through unnecessary. The DVD-Video format is also popular with the home computer market in the form of DVD-ROM and recordable DVD-R and DVD-RAM. Recordable DVD for the Home Cinema market is slowly becoming available which could lead to immense storage capacity for computers and a high quality alternative to the VHS video recorder.

The extra storage capacity on the disc can be used to store additional information not found on other formats, and these features are outlined below:  

Picture Sizes

It is possible to encode a DVD disc with multiple picture sizes to suit your system depending on the type of television you are using. The common screen size is a widescreen picture anywhere between 16:9 and the wider 2.35:1 ratio. The DVD player can output this picture to fill the full width of a widescreen 16:9 television, or can output a 'letterbox' widescreen picture when using a regular 4:3 television, though this will come with the familiar black borders above and below the picture. Some DVD's come with a 4:3 aspect ratio, either as an extra to the widescreen picture (usually on side 2 of the disc) or if the original recording wasn't filmed in widescreen.


Multiple Soundracks

Many different soundtracks can be encoded on a single DVD-Video disc. Most discs come with a stereo soundtrack that also contains surround sound information for Dolby Pro-Logic hardware. Dolby Digital is the adopted standard for digital surround sound on DVD-Video discs. Stereo and/or digital surround soundtracks can also be encoded on the same disc in different languages, in addition to the original English track. DTS 5.1 Digital Surround sound is now becoming available on UK DVD discs, further adding to the sound options available.


Alternative Soundtracks

Some DVD discs have been encoded with special soundtracks only available on DVD. The PAL release of 'Sphere' has been encoded with a recording of the lead actors - Dustin Hoffman and Samuel L Jackson - talking about the film. You watch the film in the normal way, but can hear the actors voices explaining behind-the-scenes information relating to the picture on the screen. Some discs contain a voice-over by the Director, the Editor or even the Writer of the movie you are watching.


Multiple Subtitles

Up to 32 different language subtitles can be encoded on to a DVD disc, with each being accessed at the touch of a button on the remote control.


Special Features

Including the original cinema and theatrical trailers, script notes, and behind-the-scenes documentaries about the making of the film. Some discs also contain music videos from tunes featured in the movie, and humorous outtakes that only appear on DVD. In some cases, the disc may contain scenes that were cut from the original theatrical release.


Multiple Viewing Angles

Some DVD discs have been recorded using more than one camera and the information from each camera has been recorded side by side on the disc. This allows you to select a particular view as you watch the picture. For example, a live stage show could be viewed from the front row, the back row, from a local camera concentrating on a single performer, or from a view switching between all the cameras, just like normal television.


Multiple Storylines

DVD can be encoded with different storylines or endings within the same story. When a certain point is reached, the viewer will be given options of how the story continues, with each option being selected from the remote control. Usually used in children's stories or interactive DVD's.


Alternative Endings

Some DVD's contain an ending to a movie that was deleted from the original release for one of many reasons and never made it into the final cut. If included on the DVD, you get the chance to view the original ending as the director intended. Alternative endings tend to be in the form of deleted scenes that were not used in the original theatrical release, or a choice of endings in multimedia discs.


Regional Coding

At the insistance of the movie studios, the DVD format was designed with a means of controlling the worldwide distribution of discs. Every country has a different release date for DVD movies, and the studios wanted to ensure that a disc released in one country couldn't be imported and played in another before its official launch. The system employed is Regional Coding, where almost every DVD-Video disc is encoded with a special code that allows that disc to be read by a DVD player from one of the 6 regions into which the world is divided. For example, Region 1 discs released in the US can only be played on a Region 1 DVD player sold in the US, and likewise with Region 2 in the UK. Of course, there are always people ready to provide ways to bypass these restrictions. Although the Region Code of the actual DVD software remains unchanged, it is possible to modify a DVD player to play two, three or all regions, either using a separate chip or (on some players) typing a special code using the remote control to access the Region Code controls. Many DVD players are manufactured with the capability to play all regions, and it is only before export to another country that the code is set for its intended destination. The act of 'chipping' DVD players is very common in the UK. All modified players have been adjusted to read Region 1 discs imported from America, due to the fact that Region 1 titles usually come out several months before the Region 2 version, and because DVD was released in America about 18 months before the UK making their catalogue of DVD titles about three times bigger than Region 2.


But not all discs contain a Region Code. Some DVD's such as music, television programmes, documentaries, specialist titles and music are not governed by the same restrictions as those imposed on Hollywood movies. These so called Region 0 discs will play on any DVD player, regardless of its own code setting.

Below is a world map showing how the world is divided: