The previous two chapters described video and audio encoding. The final quality of a media stream delivered over the network usually can be improved by judicious preprocessing. Plus, compression algorithms provide the best results with a very clean source.
To optimize the picture quality for a given stream bandwidth, a number of steps can be taken to clean up the audio and video signals before compression. Perhaps the greatest distortion that impacts upon compression codecs is noise. In general, digital sources are better than analog in this respect. A signal from a DV camera is much quieter than a VHS tape. Unfortunately you will not always have control over the source; you may have had to use archive material.