Where can I see the API or standards for working with DVRs, or how can I see the requests that are exchanged between the software and the DVR?

Question

CCTV

Essence of the question
There are DVRs in different parts of the city. Periodically, some of them quietly fall off the record. It goes online, but there is no archive. There is no way to go around them daily, as well as to manually check for the presence of a recording of each camera every day.
There is an idea to write a script that would simply poll the registrar and ask to upload a list of files for such and such a number from such and such cameras, the records themselves are, as it were, not needed, just their presence (in fact, the basic functionality is any sms).
Does anyone know either diagnostic software for this issue, or a program that could catch traffic and see requests to the registrar, or is it really smart where you can see the exchange API ???

Answer 1

I made an API for setting up registrars produced by XM (port 34567) - in python, in order to get rid of platform-dependent sish libs.
https://github.com/NeiroNx/python-dvr
In theory, the search for record files can be implemented quite easily on it (the documentation for the protocol is also there).
I also tried to do for Dahua (RVi from which they are purchased) the protocol is too binary and not clear - as a result, I scored.
I watched the traffic with Wireshark.
In fact, the 3 main mass manufacturers XM, Dahua, Hikvision, and the rest are not popular or they release frank shit that a normal installer will not install in any project. The XM and Dahua protocols are similar (some people stole software from others). It would be nice to disassemble Hikvision - I did not have equipment for traffic sniffing.

Answer 2

There is an idea to write a script that would simply poll the registrar and ask to upload a list of files for such and such a number from such and such cameras

For modern registrars, it is highly likely that this is not directly possible in this form. They write video as a continuous stream, the format of which is proprietary.
We are faced with the tasks of interpreting and correctly dividing such a stream while recovering data from video recorders.
Files, on the other hand, arise when you select a date/time range for export in the software supplied by the manufacturer.
There are registrars that store records in the form of files, but they are quite rare and usually they are older models.
You probably want the ability to check a "log", log, or similar structure if it exists on the models you're using.