| As the prevalence of network applications in recent years, people has got more and more abundant information through the network, meantime they depend on network more and more. Multimedia information is welcomed by people because it is intuitionistic, full of great information content and so on. As a result, different kinds of video services on network are rapidly developed such as network video on demand, network video phone, IPTV and so on.Steady and reliable transmission quality cannot be achieved by real channel during transmission, network congestion and network bit error both could cause information loss. At the same time, raw video data has got a large amount of information, so it is absolutely necessary to compress video data so as to carry out video transmission over bandwidth limited channel. For high compression ratio, video compression encoding standards today all adopt technologies such as motion compensation , prediction, variable length codes and so on to reduce abundant space-time relativity existing in video sequence. Reduction of redundant data make compressed video stream more sensitive to bit error and packet loss, even if single burst error has happened, it will take serious affect to natural decoding of the client and the video deconstruction quality will be rapidly dropped. As a result, QoS of video services is now attracting great attention, and it becomes one of the hot topics in video communication field.This article mainly focuses on research and development of video communication system and related problems of QoS technologies, we mainly complete some tasks as follows: Firstly, we research and develop a video server with the ability of supporting concurrent streams, It can supply the multi-users with video on demand service. We adopt TCP protocol to assure the integrative and reliable delivery of alternant command, and UDP protocol is used on video data transmission as a result of its real-time requirement, meantime video data is encapsulated on the high layer using RTP protocol before. Secondly, we research and carry out experiments to analyze the related error control technologies based on H.264/AVC such as Flexible Macroblock Order and so on. Besides a scheme adopting H.264 data partition, fragmented packet encapsulation using rtp and unequal error protection based on forward error correction are presented. The experiment results demonstrate that this scheme could reduce packet loss rate effectively, also the real-time performance is assured and the reliability is enhanced. Thirdly, we research and realize a rate control method based on feedback from receiver so as to solve the congestion problem. The server could make a decision and adjust the sending speed of video packets timely according to the packet loss rate parameter submitted by client so as to reduce the packet loss rate, help to solve congestion and improve channel efficiency. |
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