I've tested on two computers, both with ubuntu.
I'm running the server at (192.168.254.3 poe number 2)
sudo ./rtsp-server.pl -s 5554 -c 554 --loglevel 5
and feeding the stream with:
ffmpeg -re -y -f rawvideo -vcodec rawvideo -pix_fmt bgr24 -s 640x480 -i - -c:v libx264 -pix_fmt yuv420p...