VLC was reporting an error:
"Your input can't be opened. VLC is unable to open the MRL 'rtsp://usr:pwd@192.168.1.147:1050/channels/1'. Check the log for details."
I searched all I knew (google, videolan_forums, stack_overflow, etc..) where to find this log file. Several hits turned out to be irrelevant (different platforms or versions).
For VLC v3.0.3 on Mac OSX 10.13.5, the answer is:
[shft]+[cmd]+M or Menu:Window>Messages
The log is not persistent, so the window must be open when the error occurs.
Anyway, this is information I wish I had been able to find more easily. I hope it helps someone else.
Wayne