How long do security cameras keep footage?

01How long does security camera footage last? Until the loop comes around

A recorder, an NVR for network cameras or a DVR for older analog ones, writes every camera to its hard drives around the clock. It does not stop when the drives fill. With overwrite turned on, which is the usual setting, it deletes the oldest recording and writes the newest in its place, hour after hour. Figure 1 draws that drive as a ring. Our glossary entry on the network video recorder covers the box itself.

So the honest answer to how long security cameras keep footage is not a fixed number. It is however many days fit on the drive at the rate your cameras write, and that number can change without anyone touching a setting: add two cameras, or let a busy season fill the street outside, and the oldest day on the drive gets younger.

Why the clip you need is often already gone

Incidents rarely get reviewed the day they happen. A missing package is noticed when the tenant gets home; damage turns up at the monthly walk; a claim letter arrives weeks later. In Figure 1 the drive holds 28 days. The package goes missing on day 3, and on day 31 the tenant asks for the video. That morning the recorder wrote day 31 over day 3. Nothing on the screen said so.

Two settings decide when video is deleted

Overwrite. On, the recorder loops as described. Off, it stops recording when the drive is full and keeps the old video, which sounds safer but means the next incident is not recorded at all. Leave it on and size the drive instead.

Maximum retention. Many recorders also have a setting, often called expiry or maximum days, that deletes video older than a set number of days even when space is left. It is how a written policy of, say, 30 days is enforced. When both limits apply, the shorter one wins: a drive with room for 37 days and a 30 day expiry keeps 30.

02How to calculate how many days your cameras keep footage

Retention is one division. The drive's size in megabits goes on top; what all the cameras write each day goes underneath:

days = drive GB × 1,000 × 8 ÷ (Mbps × 86,400 × cameras)

Multiplying GB by 1,000 gives megabytes, and by 8 gives megabits. A camera's bitrate in megabits per second, times the 86,400 seconds of a day, is what one camera writes per day. Worked through for one camera at 1 Mbps: 1 × 86,400 = 86,400 megabits, ÷ 8 = 10,800 megabytes, or 10.8 GB a day.

Now a small building: 8 cameras at 4MP using H.265 at 15 frames per second, at an example 2.5 Mbps each, recording continuously to an 8 TB drive. Each camera writes 27 GB a day, all eight write 216 GB, and 8,000 ÷ 216 = 37.0 days. Switch the same cameras to H.264 at an example 5 Mbps and the drive holds 18.5 days. To keep 30 days at 2.5 Mbps the drive needs 216 × 30 = 6,480 GB, about 6.5 TB.

03CCTV camera storage: what makes video take more space

Four settings and one thing you do not control decide the bitrate, and the bitrate decides everything else.

Resolution

More pixels need more bits, but not in proportion: a 4K picture has four times the pixels of 1080p, and the examples above give it a bit under three times the bitrate. Pick resolution per camera from what it has to show at its distance, which our guide to how far a security camera can see and identify a face works out in pixels per foot, not by habit.

Frame rate

Thirty frames per second against fifteen adds a frame for every one recorded. Neighboring frames are mostly alike and compress well, so the bitrate often rises by less than double; the calculator doubles it anyway so the answer is not optimistic.

Codec: H.264 or H.265

H.265 is the newer standard. In the published comparison by the codec's developers, it matched the picture quality of H.264 at about half the bitrate on average. In a camera the saving varies with the scene and the settings, and the recorder and viewing software have to support it. Halving the bitrate doubles the days, which is why the codec is the first setting to check on a short-retention system. Our glossary page on H.264 vs H.265 covers compatibility.

Continuous or motion recording

A camera that records only when something moves writes far less in a quiet place. If a back hallway camera writes for a quarter of the day, the drive holds four times as many days as with continuous recording. Recorders keep a few seconds from before and after each trigger, which counts toward that quarter. The costs: anything outside the motion zones is not recorded, and rain, headlights, swaying trees and night grain can trigger it all night and eat the saving.

The scene itself

Most cameras use a variable bitrate: the encoder spends more bits when more of the picture changes. One manufacturer's white paper puts it plainly: a complex scene produces a high bitrate, motion can raise it sharply, and storage for variable bitrate is hard to predict without a margin. Figure 3 shows the same camera with the same settings in two places.

04How long should security cameras keep footage?

There is no one number that fits every property. Start from how late incidents surface where you are: if a missing delivery is reported by the next morning, a week of video covers it; if damage is found at a monthly inspection or claims arrive by letter, you need more than a month, or a habit of exporting.

Then ask the people who may set a number for you. A retention period usually comes from a specific regulator for some licensed businesses, a lease or management agreement, an insurer, or a contract with a client. Ask each of them in writing. Once a claim or lawsuit is likely, the footage related to it generally has to be kept, whatever the loop would do; talk to your lawyer about what to preserve. This is general information, not legal advice. Our guide to NYC building security rules for cameras and intercoms covers the legal side for buildings in the city.

Write the policy down in three lines: how many days, who may export video, and where exports are kept. Set the recorder's maximum retention to match if you want a firm ceiling. Then size the drive so a busy week still reaches the number. Our security camera installation work starts from that retention number and the bitrate each camera really writes, and sizes the drives from both.

05Where security footage is stored: SD card, recorder or cloud

Footage can live in three places, and each fails in its own way. A memory card in the camera holds a short loop of that one camera; the same math applies, so a 128 GB card at 2 Mbps holds about 5.9 days: 128 × 8,000 ÷ (2 × 86,400). The recorder holds the main copy of every camera. A cloud service holds whatever you choose to send it, limited by your upload speed. Figure 4 puts each through the events that actually take footage away.

06How to save security footage before it is overwritten

The loop does not care how important a clip is. The moment you hear about an incident, do this, in this order:

1. Note the camera, date and a wide time window. Start a few minutes before and end a few minutes after what you think happened. Clocks drift and people misremember times.
2. Lock the clip if the recorder can. Many recorders can protect a recording so the loop skips it. Use that first; it buys time while you export.
3. Export it. Save to a USB drive or download it from the recorder's software. If the recorder offers its own file format, include the player it provides, and export a common format too if it can.
4. Play the export on another computer before you leave the recorder. A file that will not open is not a copy.
5. Write down who exported it, when, and from which recorder and camera. Keep the original export unedited, and make any trimmed copies from it.
6. Keep two copies in two places. A USB drive in the same office as the recorder fails the same way the recorder does.

If the doors run on access control, the door log narrows the search. The time a card was used at the lobby reader tells you where to look on the lobby camera, which is one reason to plan access control and cameras together.

If the loop has already passed the incident, the video is usually gone: the recorder wrote new video over it. Recovery work is for drives that failed or were damaged before the loop reached the footage. If that is your situation, stop using the recorder and read about video footage recovery before anyone reformats anything.

07Check how long your system really keeps footage

This takes two minutes a month and catches most problems before you need the video. Open playback on the recorder and jump to the oldest recording on each camera. Count the days back to today. That is your real retention, whatever the setup sheet says.

• The oldest day matches your policy, on every camera, not just the first one.
• No camera shows live video while recording nothing. A camera can look fine on the monitor and have a gap on the drive; our page on a DVR or NVR that is not recording lists the usual causes.
• The recorder reports every drive as healthy. A failed drive in a recorder without mirroring takes its share of days with it.
• After any change, added cameras, a firmware update or a replaced drive, check again.

Questions to ask an installer about retention

1. What bitrate did you assume for each camera, and is it the average or the ceiling?
2. How many days does that give on this drive on a busy day, and at night with the picture at its darkest?
3. Is overwrite on, and is a maximum retention set to match our policy?
4. Are the drives mirrored, and what is the usable capacity?
5. What is on the UPS: the recorder, the PoE switch, the modem?
6. Which cameras have a second copy, and where does it live?
7. Who can export video, and how do we lock a clip so the loop skips it?

FAQQuestions about how long cameras keep footage

Sources

• Ohm, Sullivan, Schwarz, Tan and Wiegand, 2012"Comparison of the Coding Efficiency of Video Coding Standards, Including High Efficiency Video Coding (HEVC)", IEEE Transactions on Circuits and Systems for Video Technology, vol. 22, no. 12. Source of the finding that H.265 matches H.264's subjective quality at about 50 percent less bitrate on average.
• "Bitrate control for IP video"A camera manufacturer's white paper. Source for variable bitrate rising with scene complexity and motion, and for variable bitrate storage needing a margin because it is hard to predict.
• Security Magazine, "Finding Storage Solutions for Day-to-Night Surveillance", 2012Trade article. Source for low light raising camera gain and noise, which can double H.264 bandwidth and storage and set off motion recording.
• ONVIF Profile GIndustry specification for cameras that record to their own storage and let a recorder retrieve that video, the basis for card recording in Figure 4.
• IEC 80000-13Defines the binary prefixes (a tebibyte is 2⁴⁰ bytes) that explain why some menus show fewer terabytes than the drive's label.
• The arithmetic on this pageEvery retention, storage and card figure comes from the formula in section 02: days = drive GB × 1,000 × 8 ÷ (Mbps × 86,400 × cameras). Example bitrates are labeled as examples wherever they appear.