Comparison Dahua NVR2108-8P-4KS2 vs Dahua DH-NVR4108-8P

The type primarily determines the type of cameras with which the recorder is compatible.

— Analog DVR. Devices of this type can only work with traditional surveillance cameras that output video in analogue format (usually via a BNC interface, see below). Despite the emergence of more advanced options, such cameras are still very popular due to their simplicity, low cost and reliability of video transmission. The recorder itself may have a LAN network interface and work as a network device, but it is not compatible with IP cameras.

— Digital NVR. NVR type recorders are designed to work with IP cameras connected via a local computer network. These cameras are more advanced than traditional analog cameras and support more advanced features. The main disadvantage of NVR is the rather high load on network equipment when transmitting streaming video; this can lead to interference and failures, especially when there is a large flow of other traffic on the network.

— Hybrid HVR (HDVR). Hybrid devices that combine the capabilities of DVR and NVR and can work with both analog and IP cameras. This expands the possibilities for building surveillance networks, allowing you to combine the advantages of both types of cameras and mutually compensate for the shortcomings. However, such equipment is not cheap.

— PTZ support. Compatibility of the recorder with cameras that have the PTZ function — “pan, tilt, zoom”, that is, the ability to rotate and tilt the lens, as well as zoom in / out. PTZ support allows you to control these functions through the DVR. In analogue cameras, the RS-485 port is used for its operation (see "Additional connectors").

— Responding to movement. A function that allows the DVR to recognize movement in the frame. Specific ways of using this function can be different: automatic start of recording, setting a timestamp (if the video is being recorded continuously), signaling an alarm output, notifying the operator, etc. Note that motion sensors can also be installed in the surveillance cameras themselves; however, the presence of this function in the recorder eliminates the need to specifically look for such cameras (which usually cost a lot).

— Face recognition. This term refers to the extended possibilities for working with the faces of people caught in the frame. Recorders with this function, usually, are able not only to determine the presence of a face in the frame, but to recognize its characteristic features, save the resulting “portraits” and compare them with the database stored in memory. The latter, in turn, allows you to identify people and opens up a number of additional features. A specific set of such features should b...e specified separately, here we will give a few examples. So, in many models, the face recognition system allows you to quickly search for a person in the video archive, eliminating the need for the user to personally view large volumes of video materials. Using such a system, you can record the time of arrival and departure of employees to work, as well as automatically save information about the visits of third-party visitors. Facial recognition can be added to the lock on key cards — and an attacker will not be able to open such a lock, even if he takes possession of the card. There are also more complex and advanced features — for example, the creation of groups of employees with different access rights, with access restriction and/or an alarm when an outsider appears in a prohibited area for him.

— PoC power. An analogue of the PoE technology described above, used in traditional surveillance cameras (so-called AHD). Allows you to supply power to such a camera from the registrar through the same coaxial cable that is used to transmit the video signal; this greatly simplifies the connection and increases the reliability and security of the entire system. So, when installing the camera, it is enough to lay only one wire, while its operation does not require accumulators / batteries, which can sit down at the most inopportune moment.

— Wi-Fi. In registrars, the built-in Wi-Fi module is most often used for two tasks: to work with IP cameras that support such communication, and to connect the registrar itself to a local network (or even the Internet) via a wireless router / access point. And in models with a mobile application (see below), Wi-Fi can also be used for direct communication with the control gadget. Anyway, such a connection allows you to do without fuss with wires and connectors. The disadvantages of this feature include perhaps a slight increase in price compared to analogues without Wi-Fi, but this moment often turns out to be almost invisible against the background of the total cost of the registrars themselves.
Also, the specific supported communication standard can be specified in the characteristics — usually Wi-Fi 4 (802.11n) or Wi-Fi 5 (802.11ac). In this case, the differences between them are most often not fundamental: modern Wi-Fi modules, usually, support several standards at once, so there are no problems with compatibility, and the connection speed is usually more than sufficient to work as intended.

— Wi-Fi ready. This marking means that the recorder does not have a built-in Wi-Fi module (see above), but can use such a connection when an external adapter is connected (usually not included in the standard package). Theoretically, this configuration should provide additional convenience: the user can choose whether he needs Wi-Fi functionality in this particular registrar, and if in doubt, you can purchase the device itself without overpaying for wireless capabilities, and buy the adapter later if necessary . However, in fact, Wi-Fi ready models are extremely rare these days: most buyers decide whether they need wireless when planning their surveillance system, and built-in Wi-Fi modules are not that expensive, especially compared to the total cost of recorders.

— Mobile app. The ability to work with the registrar through a mobile application installed on a smartphone, tablet or other similar gadget. In this case, specific formats for connecting to a controlling gadget can be different: direct connection via Wi-Fi, work via a local network, or even remote access via the Internet from anywhere in the world; Often multiple options are supported. All these details should be specified separately, as well as the specific functionality of the mobile application. However, usually, this functionality is quite extensive, it provides access, if not to all, then at least to the most important functions of the registrar. So, from a smartphone / tablet, you can view footage and live broadcasts from cameras, copy (and sometimes delete) recordings, change many settings, etc. Control applications are usually released for both iOS and Android, so they can be install on almost any modern consumer-grade mobile gadget.

— Support for USB modems. The ability to use an external modem connected via USB to transfer data using the 3G or 4G mobile standard. This gives independence from wires and allows the registrar to be used even where there are no wired computer networks — of course, if there is coverage. Models with this feature usually have wired interfaces, and support for a 3G / 4G modem plays the role of a failover — a backup option in case of problems with the main connection. Note that the specific type of supported mobile network depends mainly on the modem used (the compatibility of the recorder with different models will not hurt to clarify separately, but most often this is not a problem).

— Remote control. The presence of a remote control in the delivery set of the registrar. It is often more convenient to control the device from the remote control than from a computer over the network or from your own control panel.

The maximum data stream in Mbit/s that the NVR is capable of processing when recording and displaying. The throughput parameter is specified as the maximum incoming/outgoing speed, or as the sum of incoming and outgoing streams (total throughput). It is calculated in such a way that the throughput exceeds the total flow of all IP cameras connected to the DVR, and another 25–30% is put in reserve for playing video or viewing it via network access.

Standards (codecs) used by the recorder to compress the recorded video.

This parameter is important when viewing recorded materials on another device — for example, a media centre, into which a "flash drive" with files from the recorder is inserted. For normal viewing, it is necessary that the player supports the appropriate codec — otherwise the video will be displayed with distortion or will not work at all. Technical details on various standards can be found in special sources.

Note that if you plan to view the materials on a computer, you can not pay much attention to this parameter: most modern operating systems have extensive built-in sets of codecs, and if you don’t have the right codec, you can easily find it on the Internet.

The maximum supported resolution of IP cameras with which the NVR is technically capable of working (primarily recording). With rare exceptions, devices record in maximum resolution from all connected IP cameras. However, the limiting factor here is bandwidth (see the relevant paragraph) – depending on the shooting conditions, it may not be enough.

High resolution allows you to get a more detailed image in which fine details are better visible. On the other hand, such videos take up large amounts of disk space, and their support significantly affects the cost of the device.

The largest total storage capacity with which the recorder is able to work correctly. By default, it is indicated only for internal media with a SATA interface (see above), however, in some models, data is also provided separately for external devices connected via eSATA.

Note that the limit on the total capacity follows from the fact that each individual port has its own limit on the capacity of the drive. In this case, the maximum capacity is distributed equally between the ports. This should be taken into account when choosing drives for the registrar: for example, in a 32 TB model with 8 SATA connectors, the limit for each connector will be 32/8 = 4 TB. This means that installing two internal 8 TB disks in such a registrar will not work, although their total capacity will be less than the maximum.

The maximum power that the DVR is capable of delivering per PoE output.

Such outputs are described in detail above; just briefly recall that they are Ethernet network ports, supplemented by the ability to power connected equipment directly over the LAN cable, without additional wires. As for the power of such a supply, it must correspond to the characteristics of the connected equipment; however, the term "compliant" may have different meanings depending on the PoE standard being used (see "PoE (output)").

So, if the registrar and the equipment work according to one of the active standards (802.3af, 802.3at, 802.3bt), the output power of the switch must not be lower than the power consumption of the connected equipment. At the same time, exceeding the output power is not scary — the described standards provide automatic adjustment, which allows the powered device to receive exactly as much power as needed, without overloading. But if the output is not powerful enough, it is obvious that it simply cannot provide effective work.

In turn, when using passive PoE, the output power of the power supply should ideally match the power consumption of the load as closely as possible. This is due to the fact that in such cases the power output produces a strictly defined power, with little or no matching and adjustment. And if the excess of a couple of watts, most powered devices are able to transfer more or less "calmly", then a more significant exces...s is fraught with overloads, overheating and equipment failure.

In conclusion, it should be said that if there are several PoE ports and they are used simultaneously, the available power supply per port can be noticeably less than when PoE is operating in only one connector. This point can be clarified by information on the total PoE power (see below) — this power is divided into all the ports involved. For example, if the switch has three PoE outputs, and the power per output is 60 W, then the total power can also be claimed at 60 W. Accordingly, when using PoE on all three outputs at once, the power on each of them will be less than 60/3 = 20 W. Technically, more advanced methods of power management are also possible — with "smart" power distribution depending on the needs of specific devices (relatively speaking, 30 W, 20 W and 10 W for the same total value of 60 W); but for a full guarantee, it is worth proceeding from the fact that all energy is divided equally.

Support of the registrar of the ONVIF standard.

This standard describes the protocols for the interaction of various components of a video surveillance system; a registrar that supports it will be fully compatible with other ONVIF equipment, regardless of manufacturer.