
Real-Time recording refers to recording frame rates that look smooth to the human eye.
Video is made up of frames. A frame is a single still image. Showing frames in chronological order give the appears of motion, flip-book style.
In video-speak, the frame rate is the rate at which frames are shown. In normal human terms, video looks "jerky" until you get into the upper 20 frames per second.
Normal television in the US and Japan (NTSC) uses 29.97 Frames Per Second (fps). Normal television in other countries (PAL) uses 25 fps.
The computer you are reading this on likely shows you 60 fps, often shown as refresh rate. Many computers run faster refresh rates, 120 or even higher, so that video games and other applications give a more realistic image to the viewer.
Real-Time is essentially any recording frame rate that gives the illusion of smooth video to the naked human eye. Unfortunately there's no scientific rule about this, but most experts agree that (Here's the answer!):
Real-Time = 25 to 30 frames per second.
Some experts will allow 20 frames per second to pass as 'real-time', even though most people can look at 20 fps and see the herky-jerky look of the video.
Why does 5 frames per second matter?
So glad you asked! In Digital Video Surveillance, we deal with A LOT of video. DAYS, WEEKS of video. We have to store it all on a hard drive. And, because of video compression, the difference in storage required can vary greatly. A 5 fps difference can make the difference between storing 7 days of video, or 9 days.
Or, put in more simple terms, 16-25% difference in the amount of history you can store on a system. 25% of 18 TB is 4.5 TB, a cost of about $1000.
OK, but Gryph, why are you REALLY fired up about this?
Well, I'll tell you. It's because some competitors are selling 20-25 fps as Real-Time. And they are selling it to people for whom the naked-eye judge of Real-Time is a government inspector with the power to shut their customers down.
That's all. I just don't like BS.
Real-Time = 25-30 fps. PREFERABLY 30 fps.
Gryphon MacThoy