I discussed the MD and Dahua DVR issue with tech support where I purchased my Dahua re-brand from. What they told me is that the DVR support for MD would depend on what part(s) of the ONVIF protocol the doorbell supported.
@TechBill - to clarify, in addition to not being able to do MD in the DVR, at least on mine you can't do ANYTHING but view it/record it. You can't make any image adjustments (brightness, contrast, etc.) or exposure adjustments (BLC, WDR, etc.).
It's unfortunate that we don't really know what has to happen for HikVision to think a doorbell is offline. Is it a polling timeout, or the result of status being reported by the DB1, or ???
Here's where my opinion may get contentious. I gave up on the live feed from the DB1. What I found in my initial playing around with it is that if I wanted the DB1 to work reliably as a video doorbell with MD and ring notifications going to a phone, we were best off not using the live feed. In my case, enabling the live feed would predictably lead to the DB1 being declared as offline or, more mysteriously, the DB1 configuration being changed such that motion detection was disabled. Maybe not right away, but it was just a matter of time before something would go belly up.
In my opinion, the DB1 can't adequately deal with the continuous feed. Sure, having perfect WiFi will help minimize retransmissions and stuff, but I think the issues may be more complex than that. I question whether the processor in the DB1 can really keep up with all the MD & live feed processing that's going on, leading to it occasionally going belly up. Or, maybe there are thermal issues that are exagerated by the heavy processing and the near-continuous WiFi transmission involved with live feed. Somewhere, I remember reading someone was disabling their IR LEDs to minimize thermal problems they thought they were having. Interestingly, I did informally think most of my issues were occurring either overnight (when the IR LEDs would be on), or in the morning when direct sun was hitting the DB1. It could realistically be some combination...
All I can say is that our DB1 functions flawlessly as a video doorbell as long as I'm not doing the live feed from it.