Do you really need a Real Time CCTV DVR? And what it really means?
What is real time recording on DVR units? Real time recording means that each channel on the Digital Video Recorder is able to capture and record at least 30 frames per second. This is called full motion recording. It is the same quality as watching movie on TV. Human eye see 30fps recording as perfectly fluent video. Our eyes in fact can’t see the difference between 30fps and i.e. 60fps. Real time recording is often confused with picture quality. To make it clear, FPS (frames per second) describes smoothness of video, not a picture quality. Currently most of the DVR units are advertised as “Real Time DVR”. But there are few things we should pay closer attention to. There is a real time display and a real time recording and these are two different things.
Real time display means that DVR can display video with 30fps on all channels. That means that i.e. 16 channel DVR unit can display 480fps (16 channels multiplied by 30fps 16ch x 30fps = 480fps).
Real time display DVR may also feature Real Time Recording. It means that DVR can display and record 30fps on every channel.
Not every Real Time Display DVR features Real Time Recording. Sometimes we see DVR units described like this: “16ch DVR 480/120fps” which means that DVR displays video in real time but can capture total of 120fps on all channels. That also means that in this case DVR can record real time, but only on 4 channels (120fps/30fps=4 channels).
On the other hand every Real Time Recording DVR features Real Time Display. So when looking for Real Time DVR we need to make sure that it is real time dsplay and real time recording.
Another little dirty trick is recording resolution when describing maximum Frames per Second for DVR unit. Most of DVR units on the market advertised as real time can display and record picture real time but only in CIF resolution 320×240. CIF resolution is considered low or standard resolution and it equals 240TVL. So recording at this resolution will significantly lower picture quality. If we have 480 or 540 or even 700TVL CCTV Cameras, but our DVR records in CIF resolution, than there is really no difference between using i.e. 700TVL Camera vs. 340TVL Camera. We can’t use full potential of high resolution security cameras if we record with CIF resolution. Unfortunately most of the CCTV Video Recorders is able to record full motion video only in CIF resolution. Usually we can change the recording resolution to D1 640×480, but it will automatically reduce recording FPS. On average DVR able to record real time in CIF resolution can only record 7.5FPS with D1 Resolution. So if we really need real time recording DVR we should make sure that “Real Time” applies to Recording with D1 resolution.
Now, after I explained all about real time recording, time to ask a question: Do I really need Real Time DVR?
The answer is “No” in 95% cases. Industry standard for surveillance video is around 5fps. It is sufficient for all residential and most of commercial CCTV installations. The only time we may need Real Time recording is when we need to capture fast moving objects with the details. Examples are: cashier both, casinos tables, jewelry store etc. For all other application Real Time recording is absolutely not necessary. It is not only costing much more to get appropriate DVR, but also real time recording dramatically reduces recoding time. When we set our DVR to record 7.5fps on every channel we can fit 4 times more data (recording time) than when we set DVR to real time recording. So instead of getting only 1 week of recording we can get 4 weeks with lower fps setting using same size hard drive. Many people would say, that recording with lower than real time resolution makes video choppy, but we need to remember that this is surveillance video, not a movie. With 7.5 or even 5fps we are still capturing all the important details and can provide sufficient video evidence for law enforcement agencies.
So before selecting Digital Video Recorder for your new project, consider if real time D1 recording unit is really a necessary choice.
