Empty Video output despite active stream

I finally fixed the issue (see the Cornell BirdCam at https://reefcam.tv/).

I had to change the rtpTransportMode under the RTSP properties for the stream file from the default (UDP) to RTP. This solved the issue. My guess was that the firewall was blocking the UDP ports. By not using UDP we avoided being blocked on those ports. However, I’m not sure if this was exactly the reason.

I had the idea to change the rtpTransportMode based on these threads.