How fast should by computer be to run 6 cameras in 640x480?

Question

(transferred from UserFeedback) Motion is great. I used Motion in version 2.6 to set up a simple surveillance box. But still a question: I want to run six cameras (with two impact vcb cards). This should work with round robin if i understood correctly. But how fast should my box be to capture mpeg video from an average of 3 cameras continously (in about 600x500 resolution)? Any idea from your experience?

Environment

Motion version:	3.1.17
Libraries:
Server OS:

-- KennethLavrsen - 09 Nov 2004 for ThorstenKutska - 08 Nov 2004

Answer

It is difficult to answer very exact. But let me try and come with some general advice.

Let us start with the video card. You want to use a standard BT878 based capture card with only one BT878. This means that you will need to run with the Round Robin feature to run two or more cameras on the card. This in itself limits very much the framerate. If your cameras are pretty professionel and can be syncronized then you can actually jump directly from camera to camera and get a very good framerate. But with unsyncronized cameras the video card needs to syncronize each time you change input which means you must skip 1-4 frames at each shift in practical. This means that you get your framerate down in the 2-5 frames per second range.

This is actually not too bad for surveillance. Most professionel systems operates at this low framerates.

If 3 of your 6 cameras are picking up motion simultaneously and the framerate is only a few frames per second then it is possible with a normal modern desktop. You need enough RAM to make sure Linux never uses harddisk swap.

It is important to limit the number of operations the computer has to do per detected frame. If you save jpegs and mpegs and run a script for each detected frame Motion will not be able to keep up. Mainly because of I/O. And you need to limit the pre_capture to 1-3 frames max.

If you choose to use framegrabbers that can handle 25 or 30 fps and with one BT878 per channel then you will need a very powerful machine to handle this many cameras. But for surveillance you really do not need many fps to capture action. What is much more important is to have good cameras that take sharp pictures with the available light. And maybe even experiment with extra light.

Hope this gives an idea.

Otherwise feel welcome to continue this topic.

-- KennethLavrsen - 09 Nov 2004

Ok, thanks. When you said "modern desktop" did you mean like 2.5+ GHz class?

-- ThorstenKutska - 10 Nov 2004

Something up there. I run 8 cameras at 320x240 on a 1.8 GHz with 512 MB RAM. And the same server runs this TWiki and a few other things. You should not need dual CPU and 15000 rpm SCSI disks. Just a normal reasonably new standard office type machine with enough RAM like 512 MB and a normal IDE disk.

-- KennethLavrsen - 10 Nov 2004

This gives me a pretty good impression. Thanks again for the quick answers.

-- ThorstenKutska - 12 Nov 2004