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.
Highlights
H.264/AVC standard is widely used in video streaming, video communication, and various mobile video applications due to its high compression efficiency through the use of many advanced tools
For down-sampling, the algorithm based on the Sine-windowed Sinc-function is applied where a set of seven filters is used to support the extended range of the spatial scaling ratio
The main contribution of this article is a real-time bitrate control algorithm using spatial down-sampling for the low bitrate encoding
Summary
H.264/AVC standard is widely used in video streaming, video communication, and various mobile video applications due to its high compression efficiency through the use of many advanced tools. The target bits are allocated at the frame-level or the macroblock-level by considering the fullness of the output buffer and the encoding complexity. In addition to ROI-based methods, a new R-D model, along with frame skipping and bit-allocation schemes, using various perceptual metrics that are based on the characteristics of HVS, is proposed [14-19]. When the target bitrate is not satisfied, even with the maximum QP value, the conventional rate control cannot avoid a sudden frame drop which results in video quality degradation. This article proposes a simple but effective bitrate control algorithm that applies spatial resolution controls to the conventional QP-based bitrate control. The PSNR and VQM values with the proposed spatial resolution control scheme are improved up to.
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