| With the development of network and multimedia technology, VVoIP technology has been applied widely in applications such as instant messaging and video conference.-VVoIP is the abbreviation of Voice and Video over Internet Protocol, which includes contents about audio video coding, streaming media transmission and communication control.The AVS, approved in June 2003, is the second generation source coding standard owned by our country. Based on the AVS video coding standard, this paper mainly discusses the framework design of video/audio communication systems as well as the function design and communication process implemention of client/server side.Firstly, this paper introduces the relative theories about streaming media transmission and synchronous control, focusing on the implementation of Real-time Transport Protocol (RTP) and Real-time Transport Control Protocol (RTCP). By making use of the control messages provided by RTCP, we propose a synchronization control algorithm between video/audio media. Based on the implemention of RTP/RTCP, we can not only control the real-time transmission of video/audio data well, but also achieve the synchronization control in and between streams of video/audio media.Secondly, aiming at alleviating the negative effects of packet loss, network delay and jitter, we discusses two application level control strategies:the packet level forward error correction (FEC) method for packet loss based on packet loss prediction, and adaptive method of Jitter Buffer for network jitter. Through these methods, the video/audio communication effect of the overall system could be improved.Finally, the paper analyzes the classification of NAT traversal and the principle and implementation of NAT technology, introduces the workflow of STUN, TURN, UPnP, TCP/UDP hole punching traversal, HTTP tunnel traversal, and client side NAT module. In the end, the paper summarizes the present work and looks into the future research work. |
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