for such files. While this is an appealing concept, let's explore what it takes to put video on a CD-ROM. The Video Process The signal that emerges from a video camera, while it can be either analog or digital, is typically analog. The signal is laid down on either Downloaded from Digital Engineering Library @ McGraw-Hill (www.digitalengineeringlibrary.com) Copyright © 2004 The McGraw-Hill Companies. All rights reserved. Any use is subject to the Terms of Use as given at the website. Premises Technologies Premises Technologies analog (Betacam, VHS, S-VHS) or digital tape (D1, D2, Digital Betacam). Digital tape is a quite expensive medium, but it eliminates generational loss and, therefore, is popular in commercial video. To create a digital representation of analog video, the analog signal is typically sampled at three to four times the bandwidth of the video channel (unlike audio, which typically relies on a two times sample). As a result, the output bandwidth for digital-tape machines is quite high- 411 Mbps for D1, and 74 Mbps for D2. A single CD-ROM drive will hold approximately 650 MB of data. The best numbers available today, including optimal sampling and com- pression rates (discussed a bit later) indicate that VHS-quality record- ing requires roughly 5 MB of storage per second of recorded movie. That's 7,200 seconds for a two-hour movie, or roughly 30 CD-ROM disks. Finally, the maximum transfer rate across a typical bus in a PC is 420 kilobytes per second, somewhat less than that required for a full- motion movie. What the Market Wants, the Market Gets: Compression Growth in desktop video applications for videoconferencing, on-demand training, and gaming is fueling the growth in digital video technology, but the problems mentioned earlier still loom large. Recent advances have had an impact; for example, storage and transport limitations can often be overcome with compression. The most widely used compression standard for video is MPEG, cre- ated by the Moving Pictures Expert Group, the joint ISO/IEC/ITU