WWW: Beyond the Basics

11. Real-time Audio and Video

11.1 Introduction

Real-time audio and video applications are two important multimedia applications on today's computer networks. These applications enable efficient communications through computer networks. For example, videoconferencing enables a face to face meeting between groups of people at two or more different locations through both speech and sight. Videoconferencing can also be used as distance learning and collaborate work with remote teams.

11.1.1 Real-time Audio and Video in the World Wide Web

World Wide Web was designed to focus on static documents retrieval. These documents may include text files, images, audio and video files. Through there are some real-time applications (i.e., telephony and videoconferencing) products were made that allow users to hear and see real-time audio and video over World Wide Web, the current World Wide Web technology is unsuitable for real-time applications. The main reason is that current World Wide Web use HTTP as transfer protocol, while HTTP is based on TCP which is unsuitable for real-time applications (see section 4 for details). With rapidly growing of real-time audio and video applications, more and more researchers involve developing new World Wide Web technologies that support real-time audio and video applications. Real Time Video and Audio in the World Wide Web discusses a protocol called VDP that specialize for handling real-time video over the WWW.

This chapter provides inside looks of the networked audio and video.

11.1.2 Chapter Guide

Audio and video signals are analog signals by nature. To be transmitted, these signals must be first converted to digital form. In section 11.2 and 11.3, the concept of digitization is introduced. To reduce the transmission bandwidth, audio and video files are often compressed before transmission. The compression formats are also introduced in these two sections.

Real-time audio and video applications require large network bandwidth and low data latency. If an application involves more than two parties, then multipoint communications need be considered. Section 11.4 describes the characteristics of all major types of networks and their possible impacts on these applications.

Section 11.5 describes the telephony and videoconferencing systems. Hyperlinks are provided for readers who have deeper interests in these areas.

The information provided each section is relatively independent from the other sections. However, readers are encouraged to finish reading the sections in sequence to understand the entire concept of real-time audio and video applications for computer networks.

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Last modified: Sun Dec 8 1996