Rate–distortion model based rate control for real-time VBR video coding and low-delay communications

摘要

Rate control is an important component in a video encoder for data storage or real-time visual communications. In the paper, we will discuss the rate control in MPEG encoder for low-delay real-time video communications over variable bit-rate (VBR) channel. In low-delay video communications, the video transmission is subject not only to the channel rate constraints, but also to the end-to-end delay constraints. In the paper, we employ leaky-bucket model to describe the traffic parameters and monitor the encoder's output. First, an ad hoc bit-allocation method is introduced. Although satisfying the rate constraints perfectly, it provides the objective quality of the decoded image to be just comparable to that of CBR rate control using MPEG2 TM5. Then, a new rate–distortion model is developed, based on which an advanced rate control algorithm is designed, producing almost uniform distortion within a frame as well as consistent video quality between frames. Experimental results show that, when compared to both the MPEG2 TM5 and the proposed ad hoc bit-allocation method, the advanced rate control algorithm maintains not only a constant buffer delay, but also a stable decoded image quality in the scenario of VBR transmission.