Along with the development of science and technology, we have entered an information era in which the amount of digital data increases dramatically. Especially, the amount of digital video and audio is very large, which makes it extremely difficult to store and transport the information. It has become a big obstacle for us to access and use the information effectively. To tackle this problem, information compression is necessary. This thesis reviews the development of multimedia compressing technology comprehensively and introduces some commonly used multimedia compressing algorithms and some existing standards in detail. Based on the introduction of the multimedia compressing algorithms and standards, the thesis is mainly devoted to the study of the rate control algorithm for MPEG-4 video coding. Aiming to tackle the inherent frame-skipping problem of the current MPEG-4 rate control algorithm (VM-18), the main causes of frame skipping are analyzed and method for reducing frame skipping is proposed. Results show that the modified rate control algorithm reduces the frame skipping and increases the peak signal to noise ratio (PSNR) significantly. Besides we also devise a peer-to-peer real time transmission structure suitable for MPEG-4 video transporting over the Internet. The transmission system includes three stages: The available network bandwidth is predicted by using peer-to-peer feedback control algorithm; The bit is allocated using the object-based adaptive rate control algorithm; The video data is packaged into packets in the synchronization layer using efficient packetization algorithm. The rate control algorithm comprises two stages: the frame level rate control algorithm and the object level rate control algorithm. In the rate control algorithm, the target bit is first predicted according to the coding complexity of the frames. Then the bits are allocated among the video objects based on their coding complexities. Finally, the optimal quantization step is determined using the rate-distortion model. The quantization step derived in this way is sub-optimal in view of the overall situation. However it reduces the computation complexity greatly. Therefore it is a feasible and effective way in practice. The algorithm divides the rate control into two independent stages and thereby the optimization problem of the MEPG-4 real time video transmission is resolved simply, which is of great importance for the real time video transmission over the Internet.
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