Evidence work · hard disks taken out of CCTV recorders
A DVR writes until the disk is full, wraps round to the start again, and lays fresh video over whatever is oldest. Age decides the order and nothing else does. Nothing in it knows that one hour contains a break-in and the next an empty yard. Take the power away, wherever in Plymouth the recorder sits, and the cycle halts. After that it is bench work, carried out on a copy.
A quiet word first?
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| What shows up | What that points to | What to do |
|---|---|---|
| Clips wiped through the recorder's menu | The catalogue entry went; the pictures stayed | Unplug it, today |
| The installer reformatted the drive | An empty index written on top of the footage | Frames get carved out of the image |
| No lights, no picture, no response | The footage sits on the disk, not on the board | Take the disk out; we image it |
| The incident was a fortnight ago | The loop may have reached it already, and that can be checked | The free diagnosis answers that |
| It plays back but will not export | The USB socket has failed, or the export firmware is faulty | The clips come off our image instead |
| A solicitor or an insurer wants a copy | Exhibit bundle: native clips, MP4 versions, hashes, notes | Say so when you book it in |
Whatever arrives is booked in under a case number on the day it reaches the bench. An engineer then works out the actual fault, and that part is free. You get a plain answer on what can come off the drive and what cannot, followed by one price in writing. Nothing further happens until you have read it and agreed.
The same sentence starts every footage call here. Pull the plug, or lift the disk out of the unit. Nothing else on this page counts for as much, because a recorder still running is steadily writing over the clip you rang about.
The drive is put behind a hardware write blocker. Every sector is read out; not one byte travels back towards the disk. From the moment that copy exists the recorder ceases to matter, and everything left to do is done on the image.
A Hikvision lays down a HIKBTREE index; a Dahua keeps DHFS tables of its own. Where either still parses, clips come back carrying the camera they belong to and the time they were made. Where it does not, H.264 and H.265 frames are carved out of the image and assembled into files that play.
Thinking it over costs you nothing. Everything the drive gave up is listed for you before any invoice exists, and the bill only follows your go-ahead. Files travel back on media bought in for your job, with return carriage paid at this end, and the case stays on the bench until you confirm they open on your own computer.
About retention: no general UK statute fixes a minimum period for keeping CCTV. The figure people quote at each other traces back to data-protection guidance about not keeping footage beyond the purpose it was gathered for, and it describes no hardware at all. What sits on your particular box is settled by the number of cameras, the bitrate and the size of the drive. Assume the shorter answer.
The insurer did not ask for the footage until nine days afterwards, and the recorder had run without a break in between. The disk came out, was imaged, and its index read; the minutes that mattered were still sitting in blocks the loop had yet to reach. Two copies went out — one to watch, one for the claim file.
Frequently, yes. It hangs on one thing — whether the box was stopped before the loop came round to those blocks again. Deleting removes a line from the catalogue and nothing else. The pictures sit where they were until new video is laid over them.
Then it is gone. New frames occupy the places the old ones held, and nothing remains below them. No laboratory reverses that, ours included. It is why the first thing we ask is that you pull the plug.
Seldom. A DVR amounts to a case, a board and a hard disk, and the footage lives on the disk. The board can be beyond help without that mattering much. The disk comes out, gets imaged, and the work proceeds on the image.
Three things decide it: the size of the disk, the number of cameras feeding it, and the bitrate they are set to. A forecourt with movement all day can come round on itself within a few days. While the box runs, take it that time is against you.
Every minute the recorder runs, the clip you need moves closer to being written over, and your deadline has not moved. Start it here. The first look is free, and what you tell us goes no further.