How to calculate the hard disk capacity of surveillance video?
First, let's look at the following three related concepts:
1, IPC code stream
The code stream of the camera monitors the bandwidth of the video stream and is divided into a primary stream and a substream.
The main stream is used for storage, and the substream is generally used for previewing. This is also the main reason why the video quality during video playback is higher than the preview.
The code rate varies at different resolutions/frame rates and picture effects.
Due to the different encoding compression algorithms, H.264 and H.265 code streams are different.
At present, the mainstream coding is H.265, which saves nearly half of the transmission bandwidth and storage footprint compared to H.264.
| The relation of resolution and bit rate | |||
| Name | Resolution (pixel) | Bit rate（H.264） | Bit rate（H.265） |
| D1(4CIF) | 704*576 | 1.5Mb/s | 0.9Mb/s |
| 720P | 1280*720 | 3Mb/s | 1.8Mb/s |
| 960P | 1280*960 | 3.5Mb/s | 2.1Mb/s |
| 1080P | 1920*1080 | 5Mb/s | 3Mb/s |
| 3MP | 2048*1536 | 7Mb/s | 4.2Mb/s |
| 4MP | 2560*1440 | 8Mb/s | 4.8Mb/s |
| 5MP | 2592*2048 | 10Mb/s | 6Mb/s |
| 8MP | 3264*2448 | 12Mb/s | 7.2Mb/s |
| 4K | 3840*2160 | 16Mb/s | 9.6Mb/s |
2, hard disk capacity
That is, the storage space of the hard disk generally has 1T, 2T, 3T, 4T and 6T.
1T = 1024G, 1G = 1024M.
The capacity of the hard disk that can actually be used to store video is 90% of the total capacity, that is, the capacity factor is 0.9. Why?
Because:
The standard of the hard disk manufacturer is decimal, so 1G=1000MB=1000000K
The system uses binary, so 1G=1024MB=1048576KB
3, the number of monitoring channels
The number of surveillance cameras that need to be recorded. If 50 cameras need to save video, the number of channels is 50.
The specific calculation method is as follows:
Video storage size = primary stream (M) ÷ 8 × 3600 (seconds) × 24 (hours) × number of monitoring channels × number of recording days
Suppose the HD header of a project is H.265 format 1080P (the main stream is about 2.3M), 50 channels, and stored for 90 days.
Then the formula is as follows:
2.1 (main stream) ÷ 8 × 3600 (seconds) × 24 (hours) × 50 (monitoring channel) × 90 (video days) ≈ 102060000MB
Converted to T: 102060000÷1024÷1024≈97.33T
According to the actual capacity of the hard disk, 90% is: 97.33 ÷ 0.9 = 108.15T, that is, the 108.15T hard disk can meet the storage requirements, so the hard disk should be prepared by pressing 110T.
Note:
Because 1T=1024G=1024MB=1024Byte,
1Byte=8bit,
Therefore, in the calculation, the main code stream ,8, that is, the so-called monitoring code stream is in units of bits.
Two
Several ways to increase storage time
1. Adjust the camera to change the code rate
The fixed rate (CBR) refers to the constant rate of the IPC output;
The variable code rate (VBR) can be dynamically coded according to the complexity and motion of the monitoring scene;
For static scenes, IPC uses a very low code rate and video files are relatively small; in dynamic scenes, higher code streams are used to ensure clarity.
According to industry data, using the variable rate function, the storage time of the hard disk can be increased by about 4 times (depending on the actual use environment).
2. Motion detection video
"Motion detection", as its name suggests, is to detect moving pictures.
Motion detection recording refers to storing video only when moving objects, which can effectively improve the storage time of the hard disk. Most of the time and environment (such as night and outdoor), the monitoring screen is still, if the 24-hour timer recording, there will be a lot of useless, uninteresting video.
According to experience, after using motion detection recording, the storage time of the hard disk can be extended by more than 3 times (the specific multiple is related to the environment).
3. Expansion
Storage expansion is also one of the ways to increase the length of time. When storage expansion is enabled, the maximum length of video information storage can be extended by about 3 times.
4. Storage strategy
It can be set by the storage policy function supported by the NVR, and allocates reasonable storage space to different channels according to the importance of monitoring.
