Video storage starts with the bitrate actually recorded, not camera resolution alone. A defensible capacity estimate separates the video payload, additional data, usable disk capacity and operating reserve. It also checks whether the recorder can sustain peak ingest and playback while meeting the retention requirement.
Table of Contents
How do you calculate the video payload?
For a continuous stream using decimal units, GB/day = bitrate in Mb/s × 10.8. The factor converts bits to bytes and seconds to a day. Multiply by camera count and retention days for a simple constant-average estimate.
An illustrative system of 24 cameras, each averaging 4 Mb/s for 30 days, produces 24 × 4 × 10.8 × 30 = 31,104 GB, or 31.104 decimal TB of video payload.
| Input | Example | Limitation |
|---|---|---|
| Cameras | 24 | Count every recorded stream |
| Average bitrate per camera | 4 Mb/s | Measure representative operation |
| Recording duty | Continuous | Event-only recording needs another model |
| Retention | 30 days | A project requirement, not a legal recommendation |
| Video payload | 31.104 TB | Excludes other data and capacity losses |
Distinguish decimal TB from binary TiB when comparing operating-system displays with drive labels. A unit conversion is not missing storage.
Why are megapixels insufficient?
Resolution affects the data available to encode, but scene activity, frame rate, noise, compression settings and encoder implementation determine the resulting bitrate. Rain, foliage, low-light noise and busy scenes can change storage demand.
Axis’s stream documentation distinguishes variable, average and maximum bitrate settings and relates retention planning to storage. It also notes that a displayed raw-video bitrate may exclude transport overhead. Measure the stream that is actually recorded, not a browser preview or a different camera profile.
Keep the accepted image-quality task visible. Reducing bitrate until the capacity estimate fits can remove the detail the system was purchased to retain.
Add capacity layers explicitly
Start from video payload, then add audio, metadata, thumbnails, additional streams and other stored material. Account for filesystem and application overhead using supported sizing information.
Determine usable capacity after the selected redundancy scheme and reserved space. Do not multiply the nominal number of drives by their labels and call the result retention capacity.
For a simplified example, if an allocation policy allows recordings to occupy at most 80% of usable capacity, the 31.104 TB video-only payload requires at least 38.88 TB of usable capacity before adding other data. The 80% policy is an example assumption, not a universal recommendation.
What changes with event recording?
Model the fraction of time recorded together with pre-event and post-event buffers, overlapping events and simultaneous activity. A quiet demonstration can greatly underestimate a busy period.
Retain enough representative recordings to evaluate variation. State how event detection failure, continuous fallback and extended incidents affect retention. A reduction based on event duty is an assumption that requires operational evidence.
If several cameras record the same event, preserve that correlation in the model. Independent per-camera averages can hide a simultaneous peak affecting both bandwidth and write performance.
Capacity and throughput are separate tests
A recorder can have enough disk space yet fail under peak ingest, concurrent playback, export or rebuild activity. Specify throughput and recovery tests alongside retention.
Review network links, controller behavior and supported drive configuration. Verify how the application deletes old recordings, reserves protected evidence and reports capacity exhaustion. A legal hold or protected incident can reduce space available to normal rolling retention.
The platform failover guide addresses how secondary recording and recovery affect the evidence chain. The software procurement guide places storage in lifecycle cost.
Verify retention with actual recordings
During acceptance, confirm the oldest available recording, continuity across the period and successful export of representative evidence. Compare measured growth with the sizing model and document unexplained differences.
Retain the bitrate sample, retention assumptions and capacity calculation with the installed recording configuration. Revise the worksheet when camera profiles, recording rules or protected-data requirements change.
FAQs
How much storage does 1 Mb/s use per day?
A continuous 1 Mb/s stream uses about 10.8 GB per day in decimal units, before extra streams, audio, metadata and storage overhead.
Does H.265 guarantee a fixed percentage of storage savings?
No. Scene activity, image quality, encoder settings and implementation affect bitrate. Use measured representative recordings for the selected configuration.
Is raw disk capacity the same as retention capacity?
No. Redundancy, formatting, reserved space and other workloads reduce the space available to recordings. Verify usable capacity and operational reserve.
