TABLE OF CONTENTS H.263 provides error protection, robustness and resilience to allow accessing of video information over a wide range of transmission media. In particular, due to the rapid growth of mobile communications, it is extremely important that access is available to video information via wireless networks. This implies a need for useful operation of video compression algorithms in a very error prone environment at low bit rates (i.e. less than 64 kbit/s).
In the previous sections we studied the two important coding tools of VLC and resynchronisation markers in the H.263 codec. The former spreads the errors, and the latter tries to confine them into a small area. In this section, we introduce some more useful tools that can enhance the video quality beyond what we have seen so far. Some of these are recommended as options (or annexes) and some as postprocessing tools that can be implemented at the decoder without the help of the encoder. They can be used either together or individually, to improve video quality.
Forward error correction is the simplest and most effective means of improving video quality in the event of channel errors. It is based on adding some redundancy bits, known as parity bits, to a group of data bits, according to some rules. At the receiver, the decoder, invoking the same rule, can detect if any error has occurred, and in certain cases even correct it. However, for video data, error correction is not as...
