Research And Application Of Self-Adaptive Transportation Of Network Video

With the constant enhancement and development of the network techniques, the Internet at present has become a heterogeneous network composed by the inter-connections among various mediums, and many differences between network link and terminal devices. However, the transmission service of Best-effort mode can not ensure the QoS for video data transmission in real time. To guarantee high quality and smooth playback of the video sequence in receiver, multimedia transmission system must be designed to have high degree of adapting capacity.Among many adaptive control methods of video transmission, selective frame dropping has characteristics of low time complexity and good timeliness and can be applied in many situations. But the existing algorithms of frame dropping adopt a hierarchical speed adjusting mode, equivalent to a coarse-grain bandwidth match mode, which results in step variations of code ratio and decoding quality and could not reach a precise match between code ratio and channel bandwidth.This thesis proposed an active frame dropping algorithm to tackle the flaw of selective frame dropping algorithm. Through dropping the noncritical frames probabilistically, the proposed approach can control the code rate more accurately and therefore can make full use of the bandwidth and avoid of waste of the bandwidth. On the bases the research of the relations between frame dropping rate and decodable video frame rate and the adapting congestion control algorithm of RTP/RTCP, the dissertation provides two frame dropping rate adjusts method based on the detection and the model of the status of networks. Simulation results show that active frame dropping algorithm is an effective code rate control approach with the function of weakening network congestion, keeping network stabilization, decreasing frame dropping rate, shortening time delay of end-to-end and markedly improving the transmission quality of videos.Compared with the existing selective frame dropping algorithms, the situation of successive frame dropping may appeared in active frame dropping algorithm. The phenomenon will cause the jumps and interrupts during the playback at the receiving end and hence will affects the quality of video play. To meliorate the subjective experience of uses, the dissertation improves the active frame dropping algorithm. Through studying the relation between the control parameters and average frame dropping rate, a deterministic parameter control approach is provided and simulation results verify the effectiveness of the improved algorithm.Finally, the thesis combines active frame dropping strategy and shortening the fractional length to enhance the parallelism of data transmission. In order to ameliorate the transmission real-time demands of time delay sensitive data, the method reduces the amount of dispatching video frames to make bandwidth for extra charge caused by the increase of segmentations and achieves good performance.