This post will illustrate and hopefully clarify the aspect of frame rates in surveillance applications.  Since the origin of the motion picture, video has been captured as a series of images or pictures.  These Images are consecutively displayed at a certain rate called the frame rate.  At higher frame rates, our eyes perceive the sets of images as motion and cannot distinguish that it is just images flashing really fast on the screen.  This can be considered as real-time and is generally assumed to be 30 fps (frames per second).  Cinema films are shown at 24fps providing that smooth film look that is entertaining.  Security and entertainment however, generally do not go together.Full frame rate (real-time) is usually seen as better but this predisposition is most likely a result of the entertainment industry as well as old CCTV technology.  DVR units are able to record analog cameras at a finite resolution.  Since this resolution has been maxed out, the next step was to increase the frame rate.  This makes the video appear smoother and easier to watch.  Although good for certain applications, real-time recording is usually not necessary, but still, it has become one of the main selling points of many DVR manufacturers.

Video 1 below will illustrate the difference between three common frame rates.  For the purpose of this post, a 1.3 megapixel camera was used to capture a vehicle driving at approximately 20km/h using 1fps, 5fps and 15fps.

Video 1: Frame rate Comparison

The video shows that 1fps is not very pleasing to the eyes and 15fps is more in our comfort zone of watching videos but again this video is not for entertainment purposes.  Table 1 below provides some more details of the above video which relate more to the security industry.

Table 1: Details of Video 1 (Frame Rate Comparison)

The above table shows the redundancy of high frame rates in certain surveillance applications.  It is evident that very little benefit exists in going from 1fps to 15fps.  At 1fps, 4 good license plate images were captured and at 15fps, 84 good license plate images were recorded.  The forensic detail is the same in both cases however with the low frame rate the bandwidth and storage costs can be significantly reduced.  Fast Frame Rates are useful in applications such as Toll Highway cameras where vehicles enter the highway at high speeds or casinos where the “hand being quicker than the eye” is not desired.   For most purposes, frame rates of 5fps or less will be sufficient.

Video at low frame rates may not be as visually pleasing to the eyes but it definitely has potential to capture forensic details for a security application. Today, certain systems allow the user to setup different frame rates for recording and viewing.  They can also speed up the frame rate when an alarm occurs such as a door opening or motion detection.  Hopefully the post provided a better understanding of frame rates and how they relate to the security industry.