Digital video is video whose signal is captured in a format which is recognized by a computer. This means its signal is read with the same binary coding (0,1) as most computer applications. More importantly, digital video promises to eliminate many of the problems associated with analog video including signal path degradation and generation loss. It also blends video and audio signals more "seamlessly" than standard analog video.

Today, digital video is used in a variety of ways and is referred to in different ways. Often, we hear the term "hypervideo." Hypervideo is digital video which is internally linked to other video or media resources. Sometimes it is referred to as "interactive video." Interactive video allows for user interaction to decide the course of the video.

The main limitation of digital video on the Internet is the file size. Raw digital video files are very large. Consider this, a video image the size of an average 640X480 frame size (your standard television display) with a resolution of 24 bits per pixel (millions of colors) and a standard NTSC frame rate of 30 frames per second (fps) represents a little over 26MB of data per second of video - not counting audio. This means a 1 GB hard disk could only hold about 38 seconds of video. Obviously, reducing frame size, fps and bits per pixel makes the video more manageable. But, you compromise what viewers are accustomed to seeing when comparing this video to what's displayed on a television set.

To decrease file size, presentation windows can be varied as can frame rate. Frame sizes include 160X120 (Quarter Screen), 240X180 (Three Eights Screen), 320X240 (Half Screen), and 640X480 (Full Screen) Frame rates may range from 15 fps to 24 fps to 30 fps. Another means by which file size is reduced is through compression. Among the better compression programs available today for school use are Cinepak, Indeo, Video, and Radius. These Codecs (compression / decompression) only save what actually changes in each frame rather than each individual frame, thus creating a much smaller file and can currently achieve up to 27-1 compression.

Today, streaming technologies are becoming popular. Streaming is used for both audio and video files. Streaming digital audio and digital video are files that play while the data is being received. Unlike past digital video technologies where viewers had to wait long periods of time while the digital video had to completely download to the clientÕs computerÕs hard drive, streaming files are only downloaded as much data is needed to maintain a consistent data flow and frame rate. This usually is a little over two times the time it takes for a message to go from the server to the client. This is done so any lost data can be retrieved as needed. To play streaming files, you typically need a server that works in conjunction with a web server and the client needs a program that will play the files. For example, VOSAIC, which is a streaming video technology developed at the University of Ilinois, requires a VOSAIC plug-in. This program allows the client computer to maintain a connection with the server as well as get the lost data. The technology is rapidly changing to better serve the transfer of digital video files. For example, Apple Quicktime has developed the Internet Movie Tool. This tool falls in between streaming and fully downloading the digital video. In true streaming, the data is not saved locally, with this QuickTime tool, the digital video is eventaully saved locally, but can start playing as soon as enough data is transfered. However, again this has some limitations such as storage space and speed of transfer. As a result, Apple is constantly researching as are other technology groups for improved ways to deliver digital video. For instance, Apple QuickTime is developing new performance options for digital video. For example, "scaled" movies permit movies to be playback at different sizes and "cached" movies (Netscape 3.0 users only) - movies you have recently viewed are cached just like other documents so they do not need to re-load when you return to them. The hope is that as technology improves the transfer of digital video over the Internet, the benefits for education will be limitless.