NVR stands for Network Video Recorder and is the most current form of system for recording and storing camera video footage of an IPVS System. The 1st generation is called VCR (Video Cassette Recorder) and it uses tape. The 2nd generation is called DVR (Digital Video Recorder). It uses hard disk for storage but stays with analogue technology for video reception. NVR uses hard disks for storage and Ethernet networking for video transmission and distribution.
The most important feature of NVR is its storage capacity in terms of the period for video footage. As modern hard disks provide high capacity and are low cost, we can expect the same for NVR video surveillance systems.
Some people use NAS (Network Attached Storage) for storage of video footage. The approach will increase the cost of the system, increase the use of physical space, and increase the chance of loss of video due to the extra connection of NAS to DVR.
We employ a computer technology called RAID to reduce the chance of loss of video records due to hardware failure of hard disks. The use of RAID will reduce the probability of loss from 3.5% to 0.1% based on industry statistics. Recording by Motion Detection is a most used criterion for recording. When there is no motion detected by a camera, no recording will take place. This does not affect Live View because Live View is a display of whatever is seen by a camera in real time. Live View does not use any hard disk space for recording.
How long does the NVR store the video footage is dependent on the level of motion activities captured by the camera. For example, the period can be as long as 4 weeks or 2 months for cameras monitoring low activity areas but can be as short as 1 or 2 days for high activity areas. Of-course, this can change with the use of more or lesser hard disks. Change of lighting conditions can be interpreted by the camera as a motion. This can be filtered off but heavy filtering may skip some useful information. Filtering has to be applied with care. Playback of footage serves many purposes depending on the user's requirements. The most popular requirement is to provide evidence of an event or incidence. Other major requirements are to analyze the sequence of events or tracking path of motion.