The reader must wait for the data to download after selecting a given hypertext link. In the case of audio and video data, the delay may be significant (tens of minutes to hours, depending on network link speed, congestion, host usage, and other variables.) Also, the reader's computer must have the necessary hardware and software resources needed to properly playback the audio and render the video.
Video on the WWW is often a disappointment to most folks; they expect to see at least the production quality levels they associate with television. Typically a reader is let down to see a grainy, index-card sized image after waiting half an hour for a video from a web site. In addition, commercial television production quality is expensive. You can see the difference.
If multimedia is desired, a topic can often be presented just as an audio link rather than a video one without much loss of effect. Audio clips generally require much less time for a reader to download and can be produced with much less money.
URL: http://www.umdnj.edu/others/mm.html