Years ago, video surveillance images were recorded on video tape. Standard video, such as seen on TV, utilizes 30 images per second to give you smooth motion. However, recording at that rate might give the user only 6 hours before he had to change the tape. One solution was to cut down the number of images per second - 7.5 frames yielding 24 hours on one tape. Still, imagine having to scan 24 hours of video each day to see what might have occurred overnight - not very productive! Of course, in time, motion sensors could turn the VCR on and off and make the task a bit less daunting.
Eventually, Digital Video Recorders (DVR's) replaced this technology and brought numerous advantages - but still with significant drawbacks. The newest alternative, the Network Video Recorder (NVR) is now gaining popularity. DVR's and NVR's are similar in many ways, and yet with significant differences.
DVR's vs. NVR's
The principle similarity between DVR's and NVR's is digital recording. This enables software tools to scan recorded images more selectively than analog recordings and reduce the time for review of data. Yet this is about where the similarity ends.
DVR's are a dedicated hardware based device. They have a fixed number of recording channels and fixed resolution capability. By that we mean that for each camera, you need a separate connection on the DVR - 1, 2, 4, 8, and 16 channel recorders being common. They are also fixed resolution in that the maximum image size for the recorder is generally set to 720x480 pixels (and that being a converted image from an analog camera). Therefore, to gain positive identification of unknown people when using a DVR, a person's face would need to take up anywhere from about 1/5 to 1/6 of the height of the image, depending on the resolution of the camera.
NVR's are essentially a PC. Instead of specific recording channels, software manages the signals from various cameras in the system. NVR's thus eliminate the 720x480 image barrier of the DVR and open the way for high definition video using Megapixel IP Cameras. IP Cameras are commonly available as 1-, 3-, 5-, 10- and even 16-megapixel resolutions, and have advanced features. They send image data to the NVR in a language it understands and eliminate the formate conversion required by a DVR.
So the NVR opens the way for broader areas being covered by a single camera. By way of comparison, a 5MP camera can give the same identification quality image described above when a person's face is only 1/24 of the screen!
NVR's also elimiate point to point connections. Instead of the limitation of 4, 8 or 16 inputs, you can easily add another camera to the system when needed, and additional hard drives if required.
Planning for the Future
The world is going to IP solutions, and surveillance is no different. Not that IP is right for everyone, but we encourage you to let us review the options.