Selecting the right DVR can be quite complex. Even many in the security industry really don’t understand the technology involved. There are many factors to consider. Often, two DVRs seem to be similar, when in fact they are very different. 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). Keep in mind that many units claim to be real time because they display live video at 30 FPS on each channel. Do not be fooled by this since what is truly important is the recorded video, not the live video. A lower end unit will often record at far less than 30fps on each channel. A higher end unit will be capable of recording 30fps 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, 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’s can record CIF resolution. The higher end units can record 4CIF and D1 resolution and the highest end units can record 4CIF and D1 resolution in real time (30fps) 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.264. Compression methods can vary between security digital video recorders, there are even DVR’s that use a combination of compressions, one for recording and one for streaming over the internet. Most of the newer DVRs use H.264 which is 40% more efficient both in storage and internet streaming.
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 or 8 hard drives internally. The most advanced DVR’s will allow for RAID (redundant storage) configuration and FTP uploads. FTP uploads can be a very useful tool allowing a DVR to back up video to an off premises FTP server when an event occurs. This might allow a business to retrieve video of a thief even if he stole the DVR during the theft.
Some DVR’s 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 DVR’s 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 DVR’s 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 DVR’s 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.
Since the standalone DVR uses hardware compression, the engine of the unit is the processor (s). Though specifications between DVR’s can seem similar, the amount and quality of DSP chips is what gives the DVR it’s processing power. Lower end units will use chipsets that are found in cheap video cameras. They will not do as good a job compressing video and will affect the quality of the recorded image. The higher end units use more advanced (and expensive) chipsets that will improve video quality and the overall stability of the DVR. Also, how many chipsets are used will influence the overall performance. Lower end DVR’s will use 1 chipset to operate all channels. Higher end DVR’s may use 3 or 4 DSP chips in a single DVR. This will also determine how many functions a unit can perform at the same time. A triplex machine can only do 3 functions at one time (Live display, record, internet view) while a more advanced machine with more processing power can do 5 functions at the same time (pentaplex). Five functions would include live display, record, internet view, playback and configuration all at the same time.
These are the major items, but there are many more items that can be considered as well.