Design Of Cabac Entropy Coding Circuit In H.264/AVC

As an important part of H.264 encoder, entropy coding is conducted after the video compression to decress the bit rate further. Two entropy coding methods are used for syntax element encoding in H.264, including Context-based Adaptive Variable Length Coding (CAVLC) and Context-based Adaptive Binary Arithmetic Coding (CABAC).The percentage reduction of bit rate of CABAC could be about 10% than CAVLC. However, it is so hard to meet the demand of real-time HD video codec in software because of the high computional complexity of CABAC. On the basis of in-depth analysis and modification of CABAC, this thesis achieves an efficient hardware design of CABAC entropy coding.Firstly, the principle and algorithm flow of the CABAC are deeply researched and analysised in this thesis. The high complexity of CABAC mainly comes from two aspects:the correlation of data and the diversity of syntax elements. On the basis of comprehension of CABAC, the algorithm of key modules is optimized in order to improve the speed of coding and conductive to the realization of the hardware at the same time. Then, the thesis realizes a whole hardware implementation of CABAC entropy coding circuit and introduces the several modules in detail, which includes initialization, binarizer and context modeling, state machine of syntax element sequence control, context information management of macroblock and a binary arithmetic encoder based on a five pipeline architecture. Finally, function simulation and sequential synthesis are conducted to verify whether the entropy coding circuit of CABAC meets the design requirements or not.The CABAC entropy coding circuit in the thesis is tested by the official video test sequences of H.264 and the hardware design in the thesis can realize the ability of 1 bin/cycle stablely coding. The whole circuit use 35K equivalent logic gate approximately. Experimental results show that the CABAC entropy coding circuit can completely satisfy the 720p@30f high-definition video real-time coding requirements.