Efficient bit-rate estimation technique for CABAC

CABAC is the entropy coding method adopted in H.264/AVC main profile. The combination of CABAC and RDO can represent an improvement in bit rate of around 20%. However, the computation complexity of video encoding increases drastically. To improve the coding performance, this paper proposes a transform-domain bit-rate estimation method for CABAC, which estimates the bit-rate of coding blocks based on the quantized transform coefficients and motion vector differences. Based on the bit-rate estimation method, a fast mode decision algorithm is presented, in which the estimated bit-rate values instead of the actual ones after entropy coding are adopted to calculate the Language cost in RDO mode decision and the entropy coding is performed only on the optimal mode. Simulation results show that the proposed algorithm saves about 33% of total encoding time while the losses of PSNR and bit-rate are negligible.