There's more to digital video than thousands of channels
Analogue video recording is a mature technology and has almost reached limits determined by the laws of physics. Investments in enhancing the technology provide increasingly small returns. Digital video technology has the potential to achieve much higher levels of quality and the technology is being improved at an increasing rate. But digital video does more than provide better pictures than analogue. It has a number of unique properties that make possible applications that could not be realised using analogue video. Firstly, digital video can be manipulated more easily than analogue video. In addition to this, digital video can be stored on random access media, whereas analogue video is generally stored sequentially on magnetic tape. This random access allows for interactivity, since individual video frames are addressable and can be accessed quickly. Finally, video in digital form can be transmitted across channels unavailable to analogue video. The applications unique to digital video rely, to varying degrees, on these properties.
Digital video is more easily manipulated than analogue video. Thus digital video is used in the production of special effects. Manipulation of digital video has become so advanced that real life action can be seamlessly merged with computer generated images, as in the motion picture Jurassic Park
. Digital video manipulation technology is also used to save the expense of shooting on location. The parents of Young Indiana Jones
were shown in the first episode as filmed in the street and later when the script called for them to take a cruise their images were altered to place them at another location.
Digital video can be duplicated without loss of quality which is important for editing applications. Manipulating digital video is not exclusively the preserve of film and television producers however. Desktop video editing is possible on most high end desktop computers and many come with special hardware to digitize video. Using applications such as Adobe Premiere
, users can edit digital video on their desktop to produce digital video of modest dimensions and integrate it into other applications. Alternatively they can export an edit decision list (EDL) to conventional analogue editing equipment. Desktop computers would not be able to cope with digital video, however, unless it was easy to store and transmit.
The ability to easily store and transmit digital video is by far its most important property. It allows users to add video attachments to e-mail, sometimes called v-mail
and makes possible video telephony. Ever since the first AT&T Picture Phone was introduced at the 1964 New York Worlds Fair video-telephony has been promised. Now, a generation later, video-telephony, or video conferencing, is set to become the first widespread application of digital video. The attraction of video-telephony is due primarily to the high cost of travel. Unisys estimated that video conferencing saved the company over $3.7M in 1992 [IrCo93
]. Video conferencing is expected to become so widespread that it will have a significant impact on business air travel [Shel92
Because digital video (when compressed) can be transmitted using less bandwidth than analogue television, it is possible to provide many channels where before there were only a few or none. Residents of Greenland, for example, were without live television for many years. Because they lived so far north, live analogue transmissions from TV stations in Denmark via a satellite orbiting the equator required prohibitively expensive amounts of bandwidth. Thus, live transmissions were reserved for special occasions. Using compressed digital video, however, less bandwidth was required and regular transmission became economical. By exploiting similar technologies, cable TV systems can have enough capacity to provide hundreds of channels of digital video. In 1998 British Sky Broadcasting introduced digital television broadcasting by satellite. Using compressed video, this system has the potential to provide subscribers with hundreds of channels of television.
The low bandwidth requirements of digital video also make it easy to store and digital video can be stored on compact disc. In 1993 Philips introduced movies stored on CD that could be played on Compact Disc Interactive (CD-I) machines. Known as Video CD
, the format was agreed by a number of manufacturers and many CD players incorporating Video CD playback are now on sale. Another example of digital video storage is the Stanford University Instructional Television Network (SITN) which provides tapes of lectures to students that can be checked out at the library. Because of constrained shelf space, only the previous two weeks lectures can be stored before the tapes are reused, and the limited number of copies leads to difficulties when demand is high. Digitizing the video and storing it on servers will allow more lectures to be available, to more people, at more locations, at any time [Toba95
Video-on-demand is currently available only on an trial basis. It differs from pay-per-view (where viewers call up and gain access to a predetermined movie at a set time) in that viewers can choose the movie and the time that they see it. Bell Atlantic introduced a video-on-demand service, but initially only music videos were available. The video was delivered to the consumers homes via their copper telephone wire and normal telephone service was not disrupted. Video-on-demand services might eventually replace the trip to the video store, but only if the cost of set top decoders can be kept low. The cost of the set top box is just as crucial to Interactive Television, which exploits the random access properties of digital video. Because individual segments of video can be addressed individually, video can appear to respond to the viewers requests. This can be put to good use in educational or training applications and, to a lesser degree, in entertainment programming. The degree of interaction can vary from application to application and can range from choice of program as in video on demand, choice and order of topics as in many training applications, or even continuous interaction as in games.
Integrating digital video into interactive applications along with other media, such as sound, animation, photographs and text, known as multimedia
, is one of the most popular applications of digital video. Multimedia applications exploit all of the properties of digital video. The ease with which video can be manipulated allows low cost production of video sequences by non television professionals. The low bandwidth requirements of digital video allow it to be stored on compact discs or hard disks and to be displayed on computer screens. In addition the ease with which various segments can be accessed allows them to be integrated into highly interactive applications.
High Definition Television (HDTV) has been desirable for many years1
, but as yet is unrealised. This is not due to lack of consumer interest, or technical difficulties. On the contrary, HDTV is expected to be such a huge success that manufacturers and governments in Europe, the US, and Japan have until recently failed to agree on a standard that might give competitors in the other trading blocks an advantage.
HDTV will offer impressive quality advantages over conventional television. Images will be sharper and screens will be larger and have aspect ratios more suited to showing films
[Characteristics of Digital Video
© Colin E. Manning 1996