A real-time single-pass bit rate control algorithm in low bit-rate of macro-block layer for H.264 is presented.In order to solve the drawback of rate control model in H.264

a new concept of average pixel information bit(APIB) and the novel rate control model based on it are represented at first;then the more precise bit allocation scheme is implemented according to the coding complexity of each macro-block

and the parameters of rate control model are updated by the change of APIB adaptively;finally

the complete rate control algorithm is proposed.This algorithm is implemented in JM85(H.264/AVC)

the experimental results show that

compared to JVT-G012 in H.264

the proposed method gains 0.171kbps in control precision and 0.227dB in PSNR averagely

and controls the fluctuation on bit and PSNR precisely at the same time.