Bitrate control using a heuristic spatial resolution adjustment for a real-time H.264/AVC encoder

Abstract

Abstract Conventional bitrate control algorithms that change only the quantization parameter (QP) often suffer from quality degradation when the target bitrate is very low. Therefore, rate control algorithms that adjust spatial resolution in addition to QP control have recently been proposed, but their computations are too complex to be processed in real time. This research proposes a very simple, but effective, rate control algorithm that employs spatial resolution control as well as the existing QP-based bitrate control. The spatial resolution ratio for the best peak signal-to-noise ratio (PSNR) is calculated using a simple estimation model which defines the relationship between the PSNR and the spatial resolution at very low bitrate compression. In the proposed bitrate control algorithm, two scalability tools for adjusting the QP and the spatial resolution ratio are used sequentially to reach the target PSNR and the control decision is made for a group of pictures. Experimental results show that the proposed bitrate control algorithm approximates an optimal solution and yields a better subjective quality as well as objective quality at various bitrates compared to the conventional QP-based bitrate control algorithm. The decision of the control parameters requires very small computational complexity and is made in a completely automatic manner so that the proposed algorithm is well suited for real-time applications.