A Multimedia Communication System Based On ActiveX Control

With the development of Internet and multimedia technology , multimedia communication platform based on ActiveX control attracted more and more attention . In this paper ,our research focused on some key problems about building a multimedia communication platform based on ActiveX control .The multimedia communication platform is consist of ActiveX control , so it is a B/S architecture . We classed clients as three kinds ( teacher,multicast agent, general client ) based on their roles , so different roles have different priority and function .General multicast is replaced by multicast agent to avoid the influence of network status . The packing ,downloading and registering of ActiveX control is discussed in detail to make it work properly.As to gathering multimedia information ,we discussed the following questions: the structure of VFW , the principle of video encoding , standards of video encoding and a general process of gathering multimedia information .The transmission of multimedia streams is another important aspect . We discussed the transmission characteristics of video-audio data and control information to decide their respective transmission protocol . After analysing the structure of MCU , we changed inquirying method of MCU as event method ,so the efficiency of MCU is greatly enhanced . The relationship between the size of buffer and network delay is described ,so we can compute the size of buffer to guarantee the quality of video and audio .We created a new multimedia file format (DLT file format) to record three multimedia streams ( teacher video , screen video , audio ) .After analysing several synchronization models , we presented Object Composition Petri Net ( OCPN ) model to resolve synchronization . Finally , a brief synchronization algorithm is described .