| With the popularization of Internet technology in recent years, VOD system (Video on Demand System), which is a representative application of video and audio media transmission, has been paid more attention. VOD technology is a blending result of multiple subjects and fields such as computer technology, network communication, multimedia technology and digital compression. It is also a very important and difficult subject. Now, the coming forth of some new methods of video encoding and standards of video transmission continuously promotes the development of VOD technology, and brings the voice of the generalization of its application. Therefore, the research on the subject takes on very important practical worth.The concept and the structure of a VOD system are first introduced in this paper, and then the current status and future development about it are described. Through the reading of a great deal of the domestic and oversea literature of VOD technology, we introduce and analyze the technology of video and audio encoding, the technology of video/audio transmission and some protocols related. A new idea of weighing the efficiency of a VOD system is put forward in this paper. Under the precondition of the same quality of video transmission, the weighing standard of the efficiency of a VOD system should be to see if the system can admit more clients and give them less delay at same time.Usually people use the multicast method to enhance the system efficiency, but there are some defects in the general batching technique of the fixation of latency time in normal multicast method. So a new method of improving the whole efficiency of a VOD system through the technique of adjusting the latency time dynamically by the popularity of video streams is put forward. According to it we design a new algorithm and a demonstrable prototype VOD system is realized. The result shows that there is a less average delay and a high efficiency in the system. |
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