RTSP is a communication protocol extremely affected by firewalls, the fact that http works fine and rtsp is not, means that your firewall might be blocking that content and the rtsp feed you are getting might be configured to use UDP, in order to make sure that you are getting the rtsp data properly you should change your router configuration to not block that info, remember that rtsp can use UDP or TCP as transport layers and gets affected by the security system accordingly.
Hope this helps.
Regards!