说明：  视频会议的主入口函数，mcu.c中的代码是真个视频会议启动过程，对开发视频会议的同志应该有一定的启发意义
(Video conferencing function of the main entrance, mcu.c the code is really to start the process of video conferencing, video conferencing on the development of comrades should have inspired a certain significance)