An Adaptive Video Coding Control Scheme for Real-Time MPEG Applications
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An Adaptive Video Coding Control Scheme for Real-Time MPEG Applications Shih-Chang Hsia Department of Computer and Communication Engineering, National Kaohsiung First University of Science and Technology, Kaohsiung 824, Taiwan Email: [email protected] Received 27 February 2002 and in revised form 16 September 2002 This paper proposes a new rate control scheme to increase the coding efficiency for MPEG systems. Instead of using a static group of picture (GOP) structure, we present an adaptive GOP structure that uses more P- and B-frame coding, while the temporal correlation among the video frames maintains high. When there is a scene change, we immediately insert intramode coding to reduce the prediction error. Moreover, an enhanced prediction frame is used to improve the coding quality in the adaptive GOP. This rate control algorithm can both achieve better coding efficiency and solve the scene change problem. Even if the coding bit rate is over the predefined level, this coding scheme does not require re-encoding for real-time systems. Simulations demonstrate that our proposed algorithm can achieve better quality than TM5, and satisfactory reliability for detecting scene changes. Keywords and phrases: control strategy, MPEG, rate control, scene change, temporal correlation.
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INTRODUCTION
Recently, the video coding systems have been widely applied to digital TV, video conferencing, multimedia systems, and so forth, primarily, in order to reduce the bit rates [1, 2, 3]. It is well known that most coding techniques will generate variable bit rates in various video sequences. To transmit the variable rate bit stream over a fixed rate channel, a channel buffer is required. Therefore, the main purpose of the rate control algorithm is to prevent the buffer from overflowing and underflowing and to generate a constant bit rate for targets. To regulate the fluctuation of the coding rate, we need to allocate the compressed bit of each frame by choosing a suitable quantization parameter for each macroblock. The fundamental buffer control strategy adjusts the quantizer scale according to the level of buffer utilization [4, 5, 6]. When the buffer utilization is high, the quantization level should be increased accordingly. In a practical MPEG system, the picture type is selected from Intra, Predict or Bidirectional frames [7]. Moreover, there are many choices for macroblocks coding, including the intraframe code, the interframe code by motion compensation, or simply a replica from the previous frame. The selection of quantization scale, coding mode, and picture type will decide the coding bit rate, and consequently affect the coding quality. Due to the extremely high complexity of the optimal coding, various suboptimal solutions have been proposed [8, 9, 10]. Generally, the image quality is improved about 2 dB compared with TM5 method [11]. Based on the
model of rate distortion curve, the computation load becomes very high. In addition, if the coding result is not satisfactory, re-encoding procedures are required in these approa
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