Rate control for fully fine-grained scalable video coders

In this paper we study two rate control strategies for fully fine-grained scalable (FFGS) video coders. Usually, in scalable coders the bitstream is divided into a base layer, which is decoded by all the decoders, and one or more enhancement layers which can improve the quality provided by the base layer. In Internet video streaming it is important that the bitstream be scalable in rate, which allows a server to adapt the bitstream to changes in the available bandwidth in the network. FFGS coders allow the maximum degree of rate scalability by using scalable encoding in both the base and enhancement layers. In this paper, we propose a rate control algorithm which is based on the rate distortion characteristics of the encoded bitstream and prevents large jumps in quality. We show that due to the embedding property of FFGS encoders, we can properly select the number of bits of every layer and frame by taking into account the quality of the video sequence. In addition, by allowing a controlled amount of prediction drift, we can set the rate control of the base layer much higher and gain in some cases several dB of PSNR performance at the highest rate. Experimental comparisons are made using SAMCoW, a FFGS video coder based on the wavelet transform and motion compensated prediction, and the MPEG-4/FGS coder using the TM-5 rate control algorithm.