Research And Implementation Of Video Real-time Transmission System In Conferencing

With the development of network technology, streaming media technology and maturity of interrelated protocol standards, software conferencing system based on IP network becomes a focus of research in conferencing system field, due to its inexpensive cost and high quality service. However, the IP network can only provides"best off"services, so it is not appropriate for video real-time transmission. It often appears mosaic even pause when network congestion appears, volatile network states can also reduce the video renderer effect, so the IP network can hardly ensure quality of services for video real-time transmission. Therefore, how to implement video real-time transmission system becomes one of important issues of conferencing system based on IP network. This paper aims to build such a software system on existing network and computer equipment to find a solution to it.The contents are as follows:1. Scheme choices: According to the characteristics of video transmission on IP network, RTP/RTCP is chosen to be the transmission protocol; HAG-based mixed multicast is introduced and is used to transmit video data among users; MPEG-4 is chosen to be the code/decode standard; DirectShow technology is used to capture and render the video data.2. Detailed implementations: The primary task is to design and finish video capture filter, video send filter and video receive filter. Video send filter can encapsulate video data into RTP packets and then transmit them to IP network; video receive filter can regroup the received RTP packets when it receiving data. To improve its performances, the receive filter adopts asynchronous receiving mode, double-cache and multi-thread technology.3. Control strategies of application layer for video real-time transmission services: The paper introduces congestion control strategy on both receiving sides and sending sides and data packets repeating strategy of error control.Following jobs is done in this paper:1. After studying of transmission strategies, the filters in the process of video transmission on IP network are designed and implemented.2. HAG-based mixed multicast manner is introduced and applied, which improved the expansibility of the system.3 To ensure video QoS, control strategies on end system are designed in this...