"How much storage do I need?" is the question that always comes at the end, once the cameras and recorder have already been chosen. And it is a question with an exact answer, not an opinion: all it takes is a multiplication.
The formula
A 1 Mbps stream takes up about 10.8 GB per day. Everything is derived from that: take the bitrate of a camera in megabits per second, multiply by 10.8, and you have the gigabytes it consumes in twenty-four hours. Multiply by the number of cameras and the number of days of retention, and you have the disk size.
Why 10.8? One megabit per second is 0.125 megabytes per second; in 86,400 seconds, that makes 10,800 megabytes, which is 10.8 gigabytes. The rest is arithmetic.
Bitrates to use
With H.265 encoding and good quality cameras, realistic values for the main stream are as follows: a 2-megapixel camera is around 2 Mbps, a 4-megapixel around 4 Mbps, a 6-megapixel around 6 Mbps, and an 8-megapixel (4K) between 8 and 10 Mbps. If the cameras are still using H.264, double these values: that is the main difference between the two codecs.
Beware of one thing that inflates the numbers: the scene. A camera pointed at a still wall, with variable bitrate, stays below those values; the same camera pointed at a road with moving trees and passing headlights will stay above them. The numbers here are conservative averages.
Three examples
Villa, 6 x 4 Mp cameras, 30 days. 4 Mbps × 10.8 = 43.2 GB per day per camera. For six cameras, that makes 259 GB per day, and for thirty days, 7.8 TB. With continuous recording, you need an 8 TB disk.
Shop, 8 x 4 Mp cameras, 30 days. Same calculations: 10.4 TB. Here, it is worth considering two disks or a recorder that accepts more than one.
Warehouse, 16 x 6 Mp cameras, 15 days. 6 × 10.8 = 64.8 GB per day each; for sixteen, that makes 1,037 GB per day, and for fifteen days, 15.5 TB.
How to halve the bill (the honest way)
The first lever is event-based recording: you record only when there is motion or when the video analysis recognizes a person or a vehicle. In a quiet scene, you can easily drop to 30-40 percent of continuous recording. On a busy road, almost nothing changes because there is always movement.
The second is the dual-stream: continuous recording at low resolution plus high-resolution recording only for events. You always have everything, and you have the important parts in high quality.
The third is keeping the frame rate low where it is not needed: fifteen frames per second are enough to recognize a person; twenty-five are necessary if you need to read the license plate of a moving car. Halving the frames does not exactly halve the space, but it comes close.
What we do not recommend, however, is lowering the resolution to save disk space: a disk costs once, an unrecognizable face costs forever.
The right disk
You need a surveillance hard drive in your video recorder, not a computer hard drive. The difference is not marketing: surveillance disks are designed to write twenty-four hours a day for years, with many simultaneous streams, and they handle read errors differently because, in a video, an unreadable sector is a lost frame, not a corrupted file. A desktop disk in an NVR might work for a few months and then start having problems exactly when you need it.
Also, check how many disks the recorder accepts and whether it supports RAID: on systems where footage is evidence, a RAID 1 or 5 means that one disk can fail without taking the recordings with it.
You can find the recorders in the Professional Safire Smart NVRs, Uniview NVRs, and Professional Hikvision NVRs sections, and pre-matched systems in the professional kits. If you send us how many cameras, what resolution, and how many days you need, we will do the math for you: info@elettricity.com, 351 969 5157.