Digital video


Digital video is the digital representation in ones and zeros of a video (ie, television-like) image destined for display on a digital monitor. Because digitised video signals take up large amounts of disk space, they are usually compressed into any of a number of different formats, depending on the specific usage and storage medium.

Digital video is simply a video image represented in digital form. The real significance of digital video technology is the way it enhances the capabilities of the video format, in terms of editing, richness of content and dissemination. In addition, it offers a way to view video images on desktop PCs and over the Web.

Digital video expands the uses of video in the corporate setting. No longer limited to special occasions, it can now be used on the desktop for conferencing and on corporate Web sites, said Steve Hoffenberg, an analyst at Lyra Research.

"In the pre-Web world, what you would do is produce a canned video for a television commercial or a marketing pitch at a trade show, and the potential audience outside of the commercial was small," Hoffenberg said.

"With the Web thrown in, video is wide open for brief or extended video clips on a Web site . . . to work toward that sticky-eyeball phenomenon."

Digital video offers a number of advantages over its analog counterpart. First among them is durability. Digital media doesn't degrade when used, stored or duplicated. In contrast, analog videotapes wear down and are easily damaged when used frequently.

Menacing digital effects

Once digitised, a digital video image can be catalogued, searched and embedded with additional information. For example, a single digital versatile disc (DVD) can be embedded with numerous foreign language translations and processing effects, such as changing the contrast in a video frame. These types of effects and editing capabilities, including layering and other manipulations, are much harder to produce on film or analog video.

In terms of special effects, digital video technology lets film makers create images that would be impossible to conjure otherwise. Industrial Light & Magic, a division of Lucasfilm that produced the special effects for Star Wars: Episode I - The Phantom Menace, estimated that 95 per cent of the shots in the film used digital technology for the creation of animated characters and landscapes. The epic space odyssey was also the first feature film to premier not in film form but from a digital master file and on digital projectors.

And perhaps the biggest advantage of digital over analog is that digital video can be transported and distributed over the Internet as packet traffic in file form or as streaming media. This allows digital video content to appear as video clips and in broadcasts on Web and intranet sites. These files can be catalogued, searched and disseminated repeatedly over the Web, without deteriorating the original digital image.

Squeezing down

The biggest disadvantage of using digital video is that it occupies so much storage space. Full-motion video at VGA resolution (640 x 480 pixels per frame, or slightly better than normal broadcast TV) requires 555Mbytes per minute of video. That's 33Gbytes per hour, and even the best DVD projection system can't hold that much.

Just the thought of trying to pump that much over the Web would strain the best high-speed Internet connections. Therefore, digital video must be compressed. Unfortunately, compression can degrade the image quality, depending on the degree and method of compression.

The most common techniques use lossy compression, so called because some of the data gets lost during the process. Audio and video files can be compressed to a mere 5 per cent of their original size using lossy compression, but the data loss is usually not detectable to the human eye or ear at this level.

Another type of compression, called lossless, ensures that no data is lost but it typically offers much less compression capability and may involve significant additional processing.

Analysts say that as bandwidth availability and quality increase along with the growth in use of cable modems and Digital Subscriber Line (DSL) connections, lossy compression methods, such as the popular MPEG, will give way to streaming-video broadcasts.

"The MPEG model of slowing downloading images and then playing them is going away," said Carl Garland, an analyst at Current Analysis.

"MPEG is clunky, and that's the way it has to be now with dial-up [Internet connections]. But cable modems have the capacity to just play video over a high-speed connection. You view it the same way as cable TV."

Streaming video

A few years back, videoconferencing was the shining example of digital video technology. But videoconferencing systems, which often required special hardware, a separate conferencing room and a dedicated network connection, proved too costly for most organisations to implement.

Analysts say streaming video will pick up where videoconferencing left off, because of its convenience and lower costs. Streaming video transmits the video in real time, as it was originally recorded, without the intermediate step of compressing the image.

"Videoconferencing was streaming video, but it was done over expensive, private lines that were difficult to get to work properly and required a studio served by satellites," Garland said.

"With cheap bandwidth by a Fast Ethernet provider or through DSL, you can have that sort of quality of conference relatively cheaply over [network] lines, and you can use that line for other things when you're not in a conference."

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