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A DVR or Digital Recorder and a NVR or Network Video Recorder is like the central processing unit of CCTV Solutions. Its task is to process and store all the footage in the system's Hard Drive.
Digital Video Recorder (DVR)
Selecting the right Digital Video Recorder (DVR) can be quite complex. There are many factors to consider. The first decision to make is what level of investment you are willing to make and whether you need an entry-level unit or a high-end unit to accomplish your goals. The specifications to consider are
Frame rate refers to the number of frames a DVR can record at a given resolution each second. Real time is considered to be 30 frames per second. So in order to record real time video on 16 channels you would need a unit that can record a total of 480 frames per second (FPS). A lower end unit will often record at far less than 30 FPS on each channel. A higher end unit will be capable of recording 30 FPS on every channel.
The size of the image being recorded or displayed is the resolution. The most common resolution in the industry is CIF (360×240). To date, one of the highest recording resolution in a standalone DVR is D1 (720×480). There are also many resolutions in between. The resolution is important because the larger the image being recorded, the more detail you can determine. A 4CIF image has 4 times the detail of a CIF image. Most of the lower end DVR can record CIF resolution. The higher end units can record 4CIF and D1 resolution and one of the highest end units can record 4CIF and D1 resolution in real time (30 FPS) on each channel at the same time.
Once video is transmitted to the DVR it is compressed to conserve storage and make internet viewing more fluid. The compression used can vary from nearly no compression like wavelet or MJPEG, to the higher compression methods like MPEG4 or the current highest compression which is H.265. Compression methods can vary between security digital video recorders, there are even DVR that use combination of compressions, one for recording and one for streaming over the internet.
How much storage a DVR can hold is an important factor to consider. Lower end DVRs often allow for 1 or 2 hard drives. The more advanced units can often accommodate 6, 8 or 16 hard drives internally.
Some DVRs will accommodate synced audio recording. The lower end units will record 1-4 channels of audio, the higher end units often allow up to 16 channels of synced audio recording.
Lower end DVRs will often only offer BNC video output which would require the use of a BNC to VGA converter to view the DVR on a standard VGA monitor. The higher end units will have a VGA output as well as a BNC out. The highest end units will also have an HDMI output.
Most DVRs these days are networkable and can allow an individual to log in using internet explorer to view their security cameras. The more advanced units will have a client software that allows an individual to view multiple DVRs at the same time. This software may have features like E-mapping, camera groupings, various user levels, the ability to restrict access to individual functions and cameras for each user and more.
Network Video Recorders (NVRs)
Network Video Recorders (NVRs) are popular in the business environment. They are most likely to be used connected to an IP Camera, where content is being streamed over the network to the NVR. By using the network to connect to cameras, the advantages of an NVR include ease of scaling to more cameras (just add a camera to the network) and ease of deployment (leveraging the existing IP network). NVRs tend to have high capacities, because in the business environment, there tends to be greater requirement to record and retain more video content, for longer periods of time.