REBORN IN THE U.S.A.
Just when you thought the American audio giants had gone to rest, never to do combat again, two of the oldest and formerly mightiest have sprung to life. The occasion is no less than the development of one of the most innovative audio/video technologies ever devised.
GE and RCA have announced DVI Digital Video Interactive--a system which stores up to an hour of full-motion video and audio on a Compact Disc, with a fantastic combination of resolution, quality, and playing time.
The DVI system manages to cram the video and audio into a CD-ROM for mat. What's more, the all-digital system is interactive, allowing user control of foreground video objects, text, dynamic graphics, and audio. (At present, DVI hardware must be linked to a personal computer for interactivity, but it's hoped that all-in-one units will be developed eventually.) The demonstration at the second annual Microsoft CD-ROM conference was so surprising, and impressive, that those in attendance rose in a standing ovation.
Working in secret for three years in the David Sarnoff Research Center of General Electric's RCA Laboratories in Princeton, N.J., researchers attacked the essential problems of storing video information on CD: Too much data, too little space, and a too-slow data-read-out rate. A screen of analog video measuring 512 by 400 pixels (a pixel is the smallest basic unit of a TV picture) requires about 600 kilobytes of data per frame for digital storage (assuming 24 bits per pixel). With the NTSC Standard, 30 frames are displayed each second; this means the standard CD format has room for only about 30 seconds of digital video per disc. Further more, because the data-readout rate of the CD is only about 150 kilobytes per second, it would take over an hour for that 30 seconds of video to be read off the disc. In other words, the normal disc playing time limits the transfer rate.
Clearly, storage of raw video data was not the answer. RCA searched for a method of compressing data prior to storage, then decompressing it upon playback. At the Sarnoff Center, Larry Ryan conceived the idea of performing non-real-time compression of video frames, with custom VLSI (very large scale integrated) chips for real-time decompression. Serious number-crunching using serious (VAX) computers is done before mastering; the digital video and audio data is com pressed so that fewer bits are required for storage. The compression scheme devised by RCA is impressive indeed:
Through pyramid delta encoding, a video frame is compressed to only 5 kilobytes (except for the first frame of each new scene, which requires 15 kilobytes). The result is an hour of storage and a data rate supporting 30 frames per second.
Each time the CD is played, the compressed data must be decompressed-in real time. Two VLSI chips form the VDP (video display processor). The first chip, VDP1, is the pixel processor; it runs the decompression algorithm in software and is designed to scoot along at the healthy rate of 12.5 MIPS (million instructions per second). Its instruction set contains sever al proprietary video/graphic instructions which permit simultaneous operations; this increases processing power. A new program can be loaded in 120 µS for rapid updates, a requirement for interactivity.
The second chip, VDP2, handles output display processing. It determines the resolution modes and pixel formats. Its resolution ranges from 256 to 768 pixels horizontally and up to 512 pixels vertically. The VDP2 pixel for mats use 8, 16, or 24 bits per pixel; with the latter, any one of 16 million colors are available in each pixel. Audio chores are handled with ADPCM (adaptive delta pulse code modulation), the same method used in CD-I technology. As is the case with CD-I, DVI offers various audio bandwidths and dynamic ranges.
One DVI CD could hold about 74 minutes of video playing time. With an hour of video, the remaining disc space could be used for ADPCM audio, perhaps using its 4-bit mode (which sounds a lot better than you might think). Of course, a higher audio quality level could be traded for less video playing time or reduced video quality.
The DVI is designed with a computer bus interface compatible with several computer architectures. The first commercial incarnation of the DVI, which will reportedly be available later this year, will be two plug-in boards de signed to fit into an IBM PC AT. As with CD-ROM and CD-I products, a microprocessor-based player (with disc drive) is required.
The personal computer becomes a system which integrates software pro grams, text, graphics, sound, and full-motion video. It is the latter which differentiates DVI from CD-ROM and CD-I systems; lacking DVI's data compression techniques, the video storage of CD-ROM and CD-I is limited in playing time and quality. Even CD-V, a format designed with video in mind, offers only a few minutes of full-motion video on a CD-sized disc.
Just how good is DVI? Well, it's pretty darn good, but not perfect. Its video is indeed full-screen and full-motion, but the data-compression methods do have drawbacks. Not all scenes are encoded as well as others and particularly busy ones suffer picture deterioration. On the other hand, simpler or slower-moving scenes are very good.
DVI opens up several opportunities for product development. For example, the educational market sorely needs an affordable interactive video system (videotape is cumbersome, and video discs are expensive). Training systems must provide realism in their simulations; often the poor quality of graphics-based pictures makes them inadequate for applications such as medical, aviation, and maintenance training. DVI could remedy this.
In another application, some retail establishments are turning to in-store marketing, with video systems that al low buyers to preview their purchases.
Of course, the biggest market is the home user. GE and RCA expect that DVI prices should hit consumer afford ability by 1990. Interactive games and personal-education packages are two potential uses. If nothing else, DVI could greatly enhance the video applications of many emerging consumer products and perhaps spawn some new products of its own. I can't yet foresee what those will be, but who foresaw the laser's uses when it first appeared? There you have it. DVI brings digital video and audio to the personal computer, with enhanced interactivity, via the CD. It's a great step forward for video storage and processing and could stimulate existing CD formats.
Of course, the appearance of yet another type of CD will alarm those troubled by format overpopulation. And that's a cause for concern. To address the issue-and recognizing that any format's success hinges on its universality and its acceptance by the manufacturing community-GE and RCA have invited companies and individuals to join them in developing DVI technology. DVI is not intended to compete with existing formats or to be a new standard. Rather, it is hoped that the existing CD-ROM and CD-I standards could be stretched to allow for players incorporating DVI chips.
Then this great data algorithm could gain the acceptance it deserves. Meanwhile, it is comforting to know that technological innovation is not really dead in American audio. It's just been taking a very long nap. After CD, CD-ROM, CD-I, and CD-V with their red, yellow, green, and blue book standards, let's put DVI in a red, white, and blue book.
(by KEN POHLMANN; adapted from Audio magazine, Sept 1987)
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