| Network video conference system is the communication system, where participants of the conference can transfer video, audio and words through Internet. At the present, most of video conference systems are the centralized systems based on H.323, which require some devices such as MCU, MP, Gateway and Gatekeeper. Owing to the expensive price and the higher requirement for the config, they are popularized difficultily despite the better performance.A new low-cost and high-quality network video conference system is given and realized in the paper. N participants can be set in the server. Then the video and audio which are captured in the client will be transferred to the server. After the video and audio have been combined in the server, they will be returned to participants by multicast. Contemporarily, these combined data in the server will be pushed to the stream media server, which make other users watch the conference on real time by Windows Media Player. In the system, The combined data are sent to participants by Multicast and pushed to the stream media server by the stream media transfer protocol, which conquers the bugs where some specific hardware and fixed routeway should be provided by the network video conference based on hardware. As a result, the cost of the network video conference reduces enormously.Following the OOP, we implement the network video conference system adopting VC, DirectShow and Windows Media technology on windows platform, where the researched contents are: According to the characteristic of TCP, UDP and RTP, we reasonably choose the protocol for every phase of data transfer in the network, insure the fluency of transferring media data and the real time of response; Using the knock out technology, we peel off the object from the background; After the video and audio have been combined and respectively compressed by MPEG-4 and ADPCM technology, they are fed back by IP multicast technology, which saves the network bandwidth and optimizes the network transfer; After the combined data in the server are pushed to the stream media server, other users can also watch the conference on real time. In order to communicate among all classes, we design a basic message stack class named CMsgStation, which will be inherited by other business logic classes. Consequently, the messages sent by a class can be received immediately by other classes. The system based on COM in the paper can be upgraded and extended conveniently. |
