Joint encoder and channel rate control of VBR video over ATM networks

Rate control is considered as an important issue in video coding, since it significantly affects video quality. In this paper, we will discuss joint encoder and channel rate control for variable bit-rate (VBR) video over packet-switched Asynchronous Transfer Mode (ATM) networks. Since a variable bit-rate traffic is allowed in such networks, an open-loop encoder without rate control can generate consistent-quality video. But in order to improve statistical multiplexing gain (SMG), an encoder buffer is essential to smooth highly variable video bitstream. Due to the finite buffer size, some forms of encoder rate control have to be enforced and consequently, video quality varies. We argue that a rate control scheme has to balance both issues of consistent video quality on the encoder side and bitstream smoothness for SMG on the network side. We present a joint encoder and channel rate control algorithm for ATM networks, with leaky buckets as open-loop source flow control models. The encoder rate control is separated into a sustainable-rate control and a unidirectional instantaneous-rate control. It can improve the problem of leaky bucket saturation exhibited in previous works. Experimental results with MPEG video will be presented. The results verify our analysis and show the effectiveness of the proposed algorithm.