All of the cameras in a given system require a central video recorder in order to transmit and archive the footage they are capturing. DVRs evolved from the older VCR models, while NVRs represent the next step in the evolution of video recording technology. Here's a side-by-side look at how DVRs and NVRs compare.
Resolution of recordings
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DVRs generally offer what is known as D1 resolution, which is the traditional video quality used in closed-circuit television systems. D1 equates to a resolution of 720 x 480, which is considered the standard resolution.
NVRs, on the other hand, can record in 1080p, which is high-definition; it offers a significant improvement in video quality over the DVR system. For comparison purposes, 1080p equates to a resolution of 1920 x 1080. This results in a much clearer image.
Connecting analog cameras with a DVR system is done by way of directly plugging a BNC cable from the DVR into the camera. To connect more cameras to the DVR system, you need additional cables. DVR systems are difficult to scale up because once every BNC connection is occupied by a camera, you need to purchase an entirely new DVR before adding another camera to the system. DVRs also require that the connected cameras be in close proximity to the recorder; otherwise, the video quality begins to degrade.
The NVR eliminates these problems because it is instead connected directly to a network. IP cameras that are connected to the same network, usually by way of a PoE switch, are then able to transmit footage to the NVR. Systems based around an NVR are much easier to scale up than DVR systems, simply because they can accept a new camera once it is added to the network. In the worst case, all that would be required is an additional PoE switch. Some IP cameras are also wireless and can transmit footage to the NVR over Wi-Fi. There are no proximity limitations so long as a camera is connected to the same network as the NVR. The largest downside to an NVR system, however, is that not every IP camera will work with every NVR. So you'll need to know whether your cameras will be compatible with a given video recorder before buying.
Hybrid Video Recorders
Hybrid video recorders (HVR) are video surveillance systems that run both IP cameras and analog cameras. The versatility of these systems makes them desirable; if you're upgrading an old system and don't want to do away with all of your old analog cameras, for example, an HVR can help you make the transition and prepare for a fully IP system in the future.
Your Video Recorder
Storage capacity: For video recorders, the first question you have to ask yourself is how much storage you will need. The answer hinges on a couple of factors: the number of cameras in your system, each camera's resolution, the amount of archived footage you intend to store and how long you plan to keep recorded footage. If there are many cameras shooting in a higher resolution, the footage is going to eat up storage space quickly. You can set a video recorder to "overwrite" the oldest footage once you reach the system's capacity, but if you're not careful, the system might overwrite archived footage that you still need.
If you're running a large system that has high-quality cameras, you'll want to scale up your video recorder's storage capacity. There are a number of tools online, like this one from Supercircuits, which can help you calculate how much storage space you'll need based on the details of your system.
For example, a four-camera system that runs 24 hours a day using IP cameras, each with a 2-megapixel resolution and a frame rate of 5 fps, with video compressed into MPEG files on a NVR, would require 2.79 terabytes of storage space for footage, according to the Supercircuits calculator.
That's quite a bit of data for a moderate-size system, so it's important to plan accordingly and know what kind of capacity you'll really need. It's also wise to maintain a bit of a cushion beyond that calculated number, so you can store any particularly interesting footage you might need to refer back to.
Cloud storage: Recorded video can be stored on the cloud in addition to on your video recorder. There are a few distinct advantages to doing this, including having remote access to your videos and superior storage volume. It's important to ensure that uploading large video files are done in a manner that won't eat up all the available bandwidth and slow down your network. This can be done by either scheduling video uploads to the cloud or uploading them after peak business hours. In addition, be aware that many cloud services charge a subscription fee to use their offerings, especially to store video files in perpetuity. Make sure the company takes the appropriate cyber security measures to protect your data. On the plus side, storing videos in the cloud means that even if your hardware is damaged, stolen or tampered with, you'll still have access to your video archives.
Camera compatibility: Not every video recorder can work with every camera. Of course, DVRs require analog cameras, while NVRs use IP cameras, but the compatibility question extends well beyond that distinction. Some NVR systems, for example, are compatible with the IP cameras only from certain manufacturers and not others. When buying a video recorder, you must first make sure that the device will work with the cameras you've purchased. If you're working with a surveillance system integrator to configure your system, the cameras should be able to provide you with the necessary information.
Compression: Compression is used to eliminate unnecessary data from the footage transmitted to your video recorder, thereby saving space. Two of the more common compression techniques used for high-definition video are MJPEG and H.264. You can also use MPEG4, but the quality tends to be lower than that of MPEG4's aforementioned counterparts. Compression methods are relatively complex and vary in their applications depending on your needs and hardware. Security Info Watch has created a handy primer on compression technology if you're looking to delve into the details of video compression.
Your PoE Switches
Power-over-Ethernet switches apply only to NVR systems, but they cut out other components that would be necessary for a DVR system, like additional power sources and the BNC cables used to connect cameras to the DVR. Instead, when you connect a PoE switch to your network, you've got a power source and a means for transmitting data to your NVR all in one package. The biggest consideration when choosing which type of PoE switch to buy is the number of cameras that will be on your system. The next consideration is how likely you are to scale up in the future.
Some NVRs will have a handful of PoE ports built into them, while others will not. If you need to buy a PoE switch, the smaller ones start at around $40-$50 and offer about five ports. Each port represents a data connection and a power source for one camera. However, if your plan is to scale up and implement a very large system, there are PoE switches that feature as many as 48 distinct parts. These solutions are vastly more expensive, like this one from Netgear, which is listed at $500 on Amazon.
There are also wireless IP cameras available that require little more than mounting, but those might be less secure than wired connections. If you choose wireless, you'll need to make sure the signal can't be easily intercepted. Again, it all comes back to your particular needs and the type of system you're trying to construct.