Also, while many of these configs use the -re setting in the source, the FFmpeg developers recommend against using that for live sources, so I'd suggest first trying without that set. Keep in mind that many configs on this site were written for older versions of the plugin, and may require tweaks for the current version. If you want to share a configuration you have tested, submit a Tested Configuration Issue and it will be added to this list shortly.
If you don’t know that information, iSp圜onnect is a great place to start. ISp圜onnect maintains a large database of camera manufacturers, supported methods (MJPEG, FFMPEG, RTSP), and the necessary URLs for accessing video, audio, and stills.