How Dahua NVR works?

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Getting comfortable
Dec 11, 2019
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Can someone explain how Dahua NVR works?
It feels like magic that the small and low spec NVR can handle so many IPC camera streams, including detecting motion and IVS and alarms etc' (it also allows playback on the same time or invoking its web services).
I'm guessing the (average) NVR has less than 1 GB and not too powerful CPU.
When looking on the people who use BI, they use quite a beefy PC (16 GB RAM and 6th+ gen CPU + GPU).
Generally, it seems Dahuar NVRs and BI perform the same task (save videos and annotate motion detection/faces).

I will try to answer myself (but not sure i'm correct):
My assumption is that the NVR basically, does no work except for saving the video (without decoding/encoding the captured video) to disk. Also, it probably manage a small database to allow search operation and playback.
Motion detection/IVS is being done by the cameras and the NVR knows how to pull the information from the cameras (so the heavy work is delegated from the NVR to the cameras).
BI does not rely on the IPC and performs all the heavy lifting by itself (which requires to analyse each frame from each IPC) - this requires a strong CPU/GPU and also a lot of RAM.

Am I right?
 
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How about not quite right? The NVR is a computer with lots of functions built in that also
work with the computers inside the cameras too. The guys w/ BI have a greater functionality
over a lot of aspects that NVRs do not.
 
Your assumption is pretty accurate. The small database might be smaller than you think. It is, in effect, the file system. When there's an event reported by the camera, the NVR closes the current file and opens a new one. When the event "ends", recording switches to a new file again. I don't particularly like that approach, but that's what it is. Additionally, the NVR doesn't have to support the overhead of windows.
 
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If so, I guess the main bottleneck when working with the NVR is the hard drive read/write speed.
But still it amaze me that the NVR can record 8 or even 16 streams while allowing users to playback recordings (I didn't do the math of what is the disk max read/write speed vs what is required for recording 16 streams).
The disk we use in the NVR are mechanical disks, so i'm surprised this works (reading and writing to other disk locations).
 
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