How many frames per second do I need?

Hello again!

I just received email with question that I think is interesting:

Do I need 30fps for a camera that is recording shop entrance? My friend is suggesting model with only 15fps, is he right? - Andy S. from Prague

I admit, 25fps/30fps looks good, it's pleasant to watch smooth video like that, but your friend is right! For me you can use even 10fps and you will be happy with the footage.

Remember we are not making movies here… the goal of a surveillance solution is to: deter, protect and provide evidence to prosecute, right? Not to win an Academy Award

Just take a look at video below. It was recorded with 15 fps and then with 7fps. As you can see, you have plenty of good footage.

Also keep in mind that you don't need as many fps when you are monitoring big scenes. Video below is a good example of that.

Less fps means less bandwidth and you need smaller HDD to backup all that footage (or you can record longer).

So if you want to decide how many fps you need you should took for consideration resolution of the camera, scene size and object speed. Can you somehow calculate this? Well theoretically you can.

First coverage of your camera, to calculate this take you camera resolution and divide this by number of pixel that you need. For example:

• General surveillance aka "there was this red car" or "there where 2 people there, men I think" - it is 66 pixels per meter (1 meter is 3.3 feet)
• Forensic surveillance aka "Car with plates XX.YYYY" or good quality picture of a face - it's ~132 pixels per meter
• High surveillance aka "Blue eyes and a mole under his nose" - it's 264 pixels per meter or more

Here is sample table with horizontal coverage of different resolutions:

So as you can see for a shop entrance you can use VGA or HD IP camera and you should have a good quality footage.

Now you need average speed of a object on that scene. Here is a reference table:

And now calculate using this equation:

And you will get those numbers:

So as you can see, for a shop entrance, using HD camera (1Mpix) or even VGA with 10fps is plenty.

And this is why I can't stand projects where client asks for a 5 Mpixel cam with 20fps (sic!) for a yard surveillance :/ but well, we have this saying in Poland "Kto bogatemu zabroni" (who forbid the rich?) ;)