If you perform a search on Google with "site:ipcamtalk.com dahua anr" you'll get several results wherein no one can get it to work and complains about poor documentation. That may be why you got little or no response from forum members: either they don't know what it is, that it exists or they cannot get it to work either.
One entry from
@Andyh747 might help ==>>
ANR Setting Not Working
He states:
"OK quick update in case anyone else struggles with this. Guidance for these settings is never great so hopefully this info will help in future.
The camera was set to record motion and alarm but not continuously. I thought the setting of the ANR time on the NVR would have ensured that the camera recorded that amount but having now thought through the setup this is obviously incorrect. The setting in the NVR is just the time the NVR will download from the camera after the NVR comes back on the network. If you want missing recording and not just motion and alarm events downloaded, you must set the camera internal recording to continuous. Probably obvious to most but took me a while to figure out what was happening.
Anyway hope the above helps someone else."