命令如下：
freeswitch@telecom> conference 3500 list
9;sofia/internal/1001@192.168.1.111;2b9fdbc4-d26d-4659-a643-1cc69adea0e7;1001;1001;hear|speak|talking|video;0;0;200
7;sofia/internal/1002@192.168.1.111;49eba6b3-7a8f-40af-9559-db08c78e7739;1002;1002;hear|speak|talking|video|floor|vid-floor;0;0;200
freeswitch@telecom> conference 3500 vid-banner 9 1001@192.168.1.111
+OK
