I must recover a deleted part of recording from this hard drive.
Hard drive was used on a HIKIVISION DVR and have HikFAT filesystem.
It contanin many recording hours from some videocams.

Using DVR, client have deleted (and need to recover) just only 4 minutes from each one.
PC3ooo and also others software are unable to recognize this file system type.
(Only one seem to be DVRexaminer but is unable to recognize filesystem too)
So using R-Studio I have recovered a lot of .MPG files
After checking some of them I can see a "jump" of time when play.

Question is: have a way to recover deleted part or file was modified and overwritten with the little missing part?

Mostly that depends on further history.

Most DVRs do not erase the videos anyhow, similar to the regular file deletion.
But recording is looped, so once the drive is full, the oldest recordings are being overwritten with the newer ones.

So if the client quickly realized they've made a mistake, then chances for recovery are good. If they kept using the DVR for a longer period of time, than fits on the drive, then target data is toast.

We develop our own DVR recovery software, which doesn't rely on calendar/metadata, so should be able to pull the recordings if they are still physically available.
Please feel free to contact me, we can look into this case remotely.

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• Remote RAID, NAS, SAN, VMware, DVR (CCTV), flash and tape recovery. Data recovery support.

IF DVR Examiner did not see the FS then i guess there is only one last hope

As Dmitri said, there is some custom work here
i can offer the same if needed (but that will never be cheap, our prices for such a case starts from 1500$)

We made some custom DVR Headers for those video files where you can use with R-studio or Winhex
and will provide you with our own Video Converter Tool for the video files (when needed)

PM if needed.

good luck

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Kuwait Data Recovery - UNIX GTC
The only reason for time is so that everything doesn't happen at once. By: Albert Einstein