Design Of CABAC Decoder For HEVC

Context Adaptive Binary Arithmetic Coding(CABAC)is the only entropy codec method in High Efficiency Video Coding(HEVC).It is a typical bit-level data processing algorithm with strict serial dependencies.According to statistics data,the time cost of a CABAC decoder accounts for more than 25% timing consumption of the HEVC,and the residual coefficient decoding accounts for 60%-86% time of CABAC.In this work,I focus on the CABAC module and investigate its design technology in improve the performance.The main contribution is summarized as follows.(1)A optimized circuit for CABAC bit-streams parsing Finite State Machine(FSM)is designed,which uses one FSM to control the decision decoder and bypass decoder,sets hierarchical FSMs according to the hierarchy of the syntax elements,and controls the decoding order with additional control logic.This method reduces the cycles of frequent transition between two FSMs,and increases the speed of CABAC decoder.(2)A scanning circuit based on look-up table for residual coefficients is designed to solve the problem that the residual coefficients circuit costs many cycles.When the 2D position coordinates(position coordinates of the last non-zero coefficients)are decoded,the scanning circuit converts it into a 1D scan sequence.The experimental results show that this method only requires 3~4 cycles for a 2D position coordinates average.(3)A CABAC entropy decoder is designed and implemented,which includes bit-streams parsing FSMs,residual coefficients scanning,context modeling,arithmetic decoding,and un-binarization.Multiple standard bit-streams are used to test the function of the CABAC decoder.Verify the decoder using Field Programmable Gate Array(FPGA).The experimental results show that the ratio of the non-zero coefficient scanning cycle to the total cycle reduces by a maximum of 55.72% and a minimum of 12.75%.