https://camlytics.com/camera/generic <-- that is list of common urls those IP cameras use. Usually they do broadcast both rtsp and http. The ones which output a jpg are the ones you will need to find for your camera.
The trick is for controlling ones like pan/tilt you need to post username/password to it, but the streams are usually free to access based on firewall settings of your router.
I did a little more research, and this software actually does say it will do what I want, but I'm not 100% confident I could actually get it connected to my system. Might try it though! https://camlytics.com/calculate-vehicle-speed
base on this site https://camlytics.com/camera/azone, it using http protocol rather than rtsp. but it is strange that it work fine vlc unless it auto switch the protocol?
Did you try with the URL u/CHA0SMINT posted above? For your DVR that looks the most likely, according to:
https://camlytics.com/camera/hikvision/10
There are at least half a dozen different URL types for different models, so worth trying a few of the others if you cant find info on the exact model DVR you have.
I would be trying a few of the different combinations out in VLC player to confirm it is correct before I tried it in ffmpeg
For your model, the most likely is probably:
rtsp://username::554/Streaming/Channels/101
Change the 192.168.0.1 from the URL above for the IP address of your DVR. Substitute your username and passwords. The suffix shown as 101 is for the camera on channel 1, change to 201 for channel 2 etc etc.
There are some security camera's with that type of software build-in or run analytics software on your camera's that you put at every entry, for example: https://camlytics.com/