Summary

In this chapter we have looked at Video and Audio coding and compression techniques. We have also introduced some preliminary ideas in conferencing and conference control protocols, by virtue of their being part of one of the dominant standards for compression, namely the H.320 family: more of this in chapter six. Important lessons for people using multimedia include:

1.

Multimedia is large! The same amount of information can often be represented for human consumption in text taking far less storage or transmission than in graphical form.

2.

Multimedia is highly redundant, and compresses very successfully

3.

Human perception is frail, and cognition smart. We can take advantage of it - note that the auditory and visual systems, however, are quite different, with persistence, averaging, and so on happening at different stages in each.

4.

Users of some critical applications cannot tolerate any artifacts, and therefore prefer lossless compression - examples are typically in the area of medical imaging (Radiology, Ultrasound, Functional imaging from magnetic resonance imaging and so on).

5.

There are a number of ways to multiplex a set of media together, and a set of engineering tradeoffs associated with these. Different industries have made different choices for good reasons. However, this means that in the Internet, we have to unpick some of the multiplexes chosen in the broadcast and telephony industries before gaining the advantanges of the Internet's full generality.

6.

Last but not least, it is very important that the more sophisticated the compression technique (at least for video) the harder it is in processing terms; but decompression is massively less expensive than compression. This means that one-to-many applications are cost effective.