Video Surveillance
DVR’s vs NVR’s:
The DVR (Digital Video Recorder)
The DVR was created as a replacement for the obsolete multiplexer + VCR combination in which all recordings where done by taking a 3 hour tape at 25 images per second and recording video that was indexed and could be played back by using a multiplexer. But the maximum frame rates were only 3 images per second (ips) when recording 16 cameras. As computer processors became faster the DVR would quickly secure its place in history, for a decade it was the chosen method of security video storage because of these advantages:
- DVR’s can record up to 480 ips so that each camera on a 16 channel DVR could be recorded at 30 ips.
- Storage of 30 days became the normal and 60 or 90 days was easily achievable(as opposed to its predecessor which could only manage 72 hours)
- DVR’s had network viewing capability so you could view your stored video from anywhere in the world.
- Now virtually all recordings were done using Video Motion Detection (VMD) meaning that you only recorded when there was a change in activity saving lots of storage space.
With all of these advantages there were still down sides:
- CPU/Video cards were doing all of the compression
- Hard drives had no redundancy and were prone to failure due to their 24/7/365 usage
- Loss of image quality due to the DVR converting the image from analog to digital and then compression it so that it could fit the information on to a hard drive (storage was still expensive so high compression of the image file was necessary)
- Maximum resolution was only VGA quality (approx. 640x480)
- Analog cameras all had to be run back to the head end where the DVR was located
- Hard to upgrade and expand as the Video cards, OS and Software were proprietary.
The NVR (Network Video Recorder)
The big differences between DVRs and NVRs are a DVR digitally compresses analog video feeds and stores them on a hard-drive. In contrast an NVR stores digital images pre-compressed from an IP camera. This subtle difference is what makes the NVR such an efficient recorder.
All of the compression is being done in the field by the cameras allowing the CPU to only lay down pre-compressed files in an easily searchable format. The NVR can use a conventional computer (meeting certain minimum specifications) and is easily upgradable to provide additional storage or new functionality as features become available.
Other advantages:
- Can accommodate resolutions such as 480p, 720p, 1080p and greater (Currently up to 10 Megapixel which would be the equivalent of 2730p if it existed it the consumer world).
- Can accommodate up to 3500 ips on a single server (as opposed to 480 ips on a DVR).
- Cost of installation is reduced due to cables not having to be home run to the DVR.
- Cameras are powered via POE (Power over Ethernet) again minimizing cabling and installation costs.
- Multi-Touch Screen’s enabling a user friendly interface.
- Hot-swappable disks.
- File export function which embodies the watermarking and digital signature based on individual video images and audit trail for security.
- “Mirroring” can be used to duplicate the recording of video streams on additional Hard Drives to minimize the chance of a single point of failure; if one part goes down the other is there as a backup.
- NVRs record, replay simultaneously from a number of authorized operators spread across the network all totally independently and without affecting each other.
