|
CCTV Record Rates & Resolution explained |
 |
This page is to help you understand just what Resolution and FPS or Frames Per Second actually mean when purchasing a Digital Video Recorder (DVR) as part of your CCTV Installation.
Resolution
There are three types of DVR resolutions, these being:
- CIF (320 x230 pixels)
- 2CIF or Half D1 (720 x 260 pixels)
- D1 (720 x 520 pixels)
CIF: The lowest quality resolution at 320 x 230 pixels. Think of the picture size of an everyday 17 or 19 inch monitor on a PC - the resolutions are commonly 1024 x 768 or higher at 1280 x 1024 - these are large pictures. Now imagine the size of the image produced at CIF: 320 x 230. Very small, objects at a distance appear unclear.
2CIF or Half D1: Mid-resolution at 720 x 260 pixels - a little better.
D1: Highest quality at present with 720 x 520 pixels. This is actually equal to DVD quality. SWI Security Concepts would always recommend this, although we have installed systems with a full D1 rated DVR and used 2CIF or even CIF quality recording to get longer recording times.
CCTV DVR Frame Rates
Real-time recording is at 50 Frames Per Second (FPS). This is the number of images that are captured in the video stream every second - and this is PER CAMERA. Therefore, to record 4 cameras in real-time (at 50 FPS) you would need to multiply the FPS x No. of Cameras (4) - I.e. 100 FPS rated DVR.
A 4-Channel DVR which is only rated at 50 FPS could only ever record at 12.5 FPS. However, this is still a good frame rate as the human eye only processes around 12 frames per second anyway.
So, if you have a CCTV system with 8 cameras connected, you would need a 200FPS DVR for Real-time and with 16 cameras connected, you would need a 400FPS DVR for Real-time.
By reducing the frames per second per camera, the more recording time you would get. This is commonly what we use to calculate the size of hard drive needed.
Example - Recording times (in days) for a 500GB Hard drive and 400FPS DVR
|
Normal
Quality |
CIF |
2CIF or Half D1 |
D1 |
|
FPS |
25 |
12.5 |
6 |
25 |
12.5 |
6 |
25 |
12.5 |
6 |
|
Days |
7.5 |
15 |
31 |
5.5 |
11 |
23.5 |
4.5 |
9 |
18 |
In the above example, to record at 12.5 FPS in D1 resolution, the 500GB Hard disk would save 9 days of recording before beginning to overwrite. Therefore, if it was Company policy to keep at least 30 days of recording, you would have to consider using a 2000GB (2TB )Hard disk (for 36 days) or using CIF resolution recording at 6 FPS.
H.264 vs MPEG-4
The new video compression is now H.264. It is also known as MPEG-4 Part 10 or AVC and is set to become the new standard for video encoding. It reduces the size of a digital video file by up to 50% - this means more recording time for your Hard drive, so less cost. It also allows for better viewing across networks with faster internet streaming.
Be certain you know what to expect from your Recording Equipment
| 
CCTV Record rates
