Optimal CTU-level bit allocation in HEVC for low bit-rate applications

The coding efficiency of High Efficiency Video Coding (HEVC) outperforms all the past video coding standards. But for low bit-rate video applications, fewer bits cannot guarantee the reconstructed quality of each coding frame. Rate control is used to get better quality with fewer bits, while the bit allocation is the key of rate control. This paper proposes an optimal CTU-level bit allocation based on region classification in HEVC for low bit-rate applications. The motion regions are extracted in each frame from the CTU-level. The bits allocated to the CTUs belong to the motion regions will be calculated according to the motion vectors of CTUs and the overall frames to improve the quality of these CTUs. Finally, the R-lambda model rate control adopted in HM16.0 will be used to calculate QP of each CTU. Experimental results demonstrate that the proposed bit allocation approach can achieve an average improvement of 0.32 dB in objective quality compared with the conventional rate control adapted in HM16.0, and the subjective quality improves obviously and the accuracy of rate control is also good.