Entropy Coding

Summary

An entropy encoder converts a sequence of symbols or syntax elements into a bitstream, and an entropy decoder converts the bitstream back into a sequence of symbols. This chapter looks at where entropy coding sits in a video codec and what it achieves. High‐efficiency video coding uses a combination of fixed‐length coding, variable‐length coding and BAC for different sections of the coded syntax. The chapter also looks at the main types of entropy coding used in video codecs, and arithmetic coding in detail. It presents the details of pre‐processing. Pre‐processing can help to minimise the information to be encoded, to maximise the efficiency of context‐adaptive entropy coding and to improve computational performance. An entropy encoder can estimate or model the probability that symbol has a particular value. The chapter shows how entropy coding works in H.265/high‐efficiency video coding and H.266/versatile video coding.