Can access RTSP from VLC but not any IP viewers?

[burntoc]

Any chance you can help me understand why I CAN access RTSP directly via VLC (awesome, thank you!) but I've tried Tinycam and at least 3 other IP cam viewers that work with all of my other cameras but they tell me they cannot connect - usually saying port 554 isn't accessible on that IP even though it would clearly seem to be based upon what VLC shows? I've tried RTSP over HTTP, TCP, and UDP and none of the options work. This is the link that otherwise works:

rtsp://192.168.3.15/ch0_0.h264

Thanks for any help.