Robust Entropy Coding

The most simple of the robust entropy coding techniques is self-synchronising entropy coding, which uses one codeword as a synchronisation marker and inserts it at regular intervals in the bitstream. An error-resilient entropy coding example are the Reversible Variable Length Codes (RVLC) which are used in MPEG4's error-resilient mode. These enable the backward decoding of VLCs as well as the forward, enabling the decoder to continue until the last backwards decodable VLC on the event of an error while it was decoding in the forward direction.

Forward Error Coding (FEC) could be also classified here, as it adds redundancy after the entropy encoding stage. FEC has been long used in data communications for error detection and correction. It can be used in video communications for recovery of lost packets, but its use should be judicious, as it occupies a considerable portion of the usable bandwidth. Techniques that change the encoding design parameters so as to provide a bitstream which performs optimally for given channel error characteristics, called joint source and channel coding techniques, could be also applied at this stage.

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