Frame level rate control algorithm based on GOP level quality dependency for low-delay hierarchical video coding

Rate control plays an important role in video coding, which can minimize the distortion of compressed video with bit rate constraints. Rate control algorithm based on R - lambda model is capable of controlling the bit rate precisely for high efficiency video coding (HEVC). However, quality dependency is not considered very well in lambda-domain rate control algorithm when allocating bits and updating model parameters. This paper proposes a rate control algorithm based on group of pictures (GOP) level quality dependency for low-delay hierarchical coding structure. Firstly, the quality dependency between the current GOP and encoded GOPs mainly comes from the crucial frame (C-Frame). C-Frame guided GOP level quality dependency (CF-GOP-QD) model can be expressed by a CF-GOP-QD factor. Secondly, a CF-GOP-QD model based GOP level rate-distortion optimization (RDO) under the total bit constraints is proposed to guide the bit allocation processing, which is better than traditional bit allocation method. Experimental results show that the proposed rate control algorithm can achieve better rate-distortion performance, better visual quality and better rate control accuracy. Specifically, the proposed method shows 5.801% and 5.068% BD-rate saving on average compared against HM16.7 frame level rate control method under low-delay B and low-delay P configurations.