RTSP playback:Difference between VLC and Android's build-in OpenCore

Question

I am working on an Android app to play video stream in RTSP protocol, which provided by the Darwin streaming server.

My problem is that the RTSP stream cannot be played using Android's VideoView/MediaPlayer via some specific WiFi hotspots, e.g. at my workplace. I searched around and found that Darwin streaming server use UDP Ports 6970 - 6999 for media data streaming, and the firewall may be the problem. but the same stream can be played using VLC on PC via the same WiFi hotspot.

What's the difference between the mechanism that VLC and the Android's build-in media framework OpenCore use? Is that possible for me to write my own rtsp client with live555's openRTSP source on Android? Any help will be very appreciated.

Bolton