Introduction were looking for a disc that could contain, amongst other features, about 135 minutes of film on one side of a disc at superior quality to existing laserdiscs, copy protection, parental lock, widescreen. Until 1996, two competing optical discs formats were being developed, but their development was merged in 1996 under the DVD Forum who produce the official DVD specifications. What is DVD? In the past, DVD has stood for 'Digital Versatile Disc' and 'Digital Video Disc', but now it is simply a word in itself. DVD is an optical storage technology for any information, such as video, audio, computer data and games. Although the DVD discs are similar in appearance to compact discs (CDs), the formats, physical specifications and file specifications are very different. This is explained in ‘DVD Introduction’. This document also provides information on authoring, features, disadvantages and user requirements on one of the main application Formats - DVD Vide. It also looks at what might be in store for DVD in the future and provides links to tutorials and other web pages which may be of interest.
DVD Formats Physical Formats Application Formats
Physical Formats A DVD is an optical disc consisting of microscopic pits (called ‘marks’ on writeable discs). As the disc spins in the player, a laser beam passes over the disc and the changes in the intensity of the light reflected is converted into a digital signal. As the intensity of the reflected laser beam changes, this is converted into encoded digital signal. A DVD disc consists of two substrates (0.6mm thick) bonded together. Each side can contain two layers called ‘Layer 0’ and ‘Layer 1’ (the outermost layer). The physical format of a DVD determines the capacity of the DVD disc. DVD capacity is determined by pit size, track pit spacing and the number of layers the disc contains. See below for a current list of discs and their capacities. DVD-5 and DVD-9 are the most common formats in use. DVD-9 is best suited to DVD-Video running times longer than 133 minutes. DVD-10 is suitable for when letterbox and pan & scan versions are required on the same DVD-Video, however, if the playing time is long, the disc will need to be flipped over. DVD- 14 is no longer a common format and DVD-18 is difficult to manufacture. Data can only be written once to a DVD-R disc and it is therefore often used for archiving purposes. DVD-R (G) is for general home use and DVD-R (A) is for authoring purposes (i.e. professional use). DVD- RAM, DVD-RW and DVD+RW discs can be written to disc thousands of times.
Application Formats DVD-ROM is the base format for all DVD formats. The main application formats are DVD-ROM, DVD- Video and DVD-Audio. A DVD disc can contain a combination of two or all three of these application formats. If a DVD disc contains DVD-Video and DVD-ROM, a standalone DVD player will only read the DVD- Video portion, but most DVD- ROM drives can read the DVD-ROM and DVD-Video portions (if they are equipped with a DVD-Video decoder).
DVD-ROM DVD-Read Only Memory (DVD-ROM) is similar to CD-ROM except that it can contain much more information. The reason DVD-ROM has evolved is to meet the needs of the computer industry which required a new format that could cope with the complex multimedia applications that are being developed. DVD-ROM is used for high-speed data retrieval and is therefore suited to computer games and educational software. It is envisaged that DVD-ROM will eventually replace CD-ROM.
DVD-Video DVD-Video is an application format of DVD-ROM. The objective of DVD-Video was to provide the film industry with a replacement for Laser Disc (LD). The industry wanted a disc that with a capacity of about 135 minutes (which would allow most movies to fit on a single disc), with video quality equivalent or greater than Laser Disc. In order to fit studio quality films onto DVD discs, some form of compression must be used. MPEG-2 is the standard form of compression used. MPEG-2 If studio quality film or video was transferred directly onto DVD-Video, it would create about 200Mb of data per second. The higher the data rate used, the higher the quality of sound and audio that is stored on the DVD.
Features Superior picture quality to VHS DVD-Video has 500 lines of horizontal resolution compared to VHS which has just 240, as long as the viewer has a screen that can accommodate the high resolution. Audio Superior sound quality to CD On NTSC formats, the disc must have at least one soundtrack using Linear PCM or Dolby Digital. On PAL formats, the disc must have at least one soundtrack using Linear PCM, MPEG-1 or MPEG- 2 or Dolby Digital. Up to 8 streams of Dolby Digital multi-channel audio or Linear PCM.
Features Contd. Multiple Soundtracks/Languages A DVD can contain alternative soundtracks (up to 8 tracks) or up to 4 languages (2 tracks per language). Karaoke Track This feature enables background video pictures overlaid with the lyrics of a song. Up to 32 subtitle or karaoke tracks are available. Random access features Random access features enables multiple endings for movies or games and quizzes to be created due to seamless branching. Menus Menus allow for greater user interactivity as the user can access the menu at any stage during playback. Multiple Titles The DVD-Video can contain more than one film or programme or different versions of the main feature.