retention period
Also known as: storage duration · retention time
Retention period is the length of time recorded video is kept before it's automatically overwritten or deleted.
In video surveillance systems, retention is usually implemented through rolling recording: available storage fills up in a cycle, and once it's full, the oldest footage gets overwritten. How long that takes depends on storage capacity, resolution, frame rate, compression, and the number of channels, not on a fixed time value set in the system. Only once those numbers are known can the actual retention period be calculated.
In practice, retention is either set directly in days within the NVR or recording software, or it falls out implicitly from the chosen drive size. Event-driven recording, where footage is only captured on detected motion or a detected object, extends effective retention considerably compared with continuous recording. Bump up the resolution or add a channel later, and retention drops without that showing up anywhere obvious.
A common edge case in a data protection context: retention is closely tied to the purpose of the recording and shouldn't run longer than that purpose requires. Exactly how that should be set up in a given case depends on the specific situation and should be worked out with proper legal counsel, not copied from a rule of thumb.
What it means in practice
In practice, an unclear retention period tends to surface only after an incident, when the relevant footage has already been overwritten, or the opposite: recordings sit around for months with no clear reason. NDVDL configures retention deliberately during setup instead of leaving it to whatever drive size happened to be bought; the specific period is set by the business in coordination with its own legal counsel.
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