The frame rate you choose to record your CCTV footages will obviously be dependent on the relating application. As an example, in an office or retail store or supermarket, 2 fps will be enough, but whereas in a casino, it would demand to have around 25 fps. If your system has audio recording as well, you will need at least 12.5 fps to achieve a natural lip-sync of the voices.
Most vendors of storage facilities, will advertise their products based on GB or gigabytes. However, unless you have a good knowledge about video recording you would not likely to know how many hours of recording your storage disk would do. Many factors influence this recording hours. Frame rate and picture resolution must be taken into consideration when deciding storage needs.
Your image quality also a direct effect on the storage capacity required. The lowest resolution in common use is CIF (352×288 pixels), but 2CIF (704×288), 4CIF (704×576) and D1 (720×576) are now specified increasingly often, and there is also considerable growth in the use of megapixel cameras that, as the name suggests, deliver even higher resolutions.
As an approximated example, CIF images recorded using MPEG-4 compression would take up around 10Kb per frame, 4CIF would be around 40Kb per frame and megapixel images somewhere in the range 80 to 200Kb per each frame.
It is clearly evident that bigger image resolution consumes greater space. However, in reality, things take a different turn. You can use a few megapixel cameras to survey over a large area instead of too many low resolution cameras.
This is justified on the basis that the few megapixel cameras will capture as much if not more detail than the larger number of low-resolution cameras. Clearly, if this approach is adopted, it must be taken into account when calculating the storage capacity needed.