NetStream Object can not play RTMP format stream but keep receiving onMetaData event

Hi,

        My application is attaching NetStream object on linked video object to to play RTMP format streaming. After the connection was built, the display area of linked video object shows the very first frame of the streaming. However, it stopped at the frame and the display area was no longer updated. On the other hand, the application kept receiving onMetaData event of the NetStream. I tried both ffmpeg and vlc player and found that these two can successfully play the RTMP streaming. The strangest part of this issue is that some of the RTMP streaming can be played but others can't. It also behaves differently in different browsers and different computers. Can anyone help me? Thanks.