A hybrid DVR is a DVR that can accept more than one type of video signal. The three most common video signals on the market today are analog, HD-SDI, and IP. It is advantageous to have a hybrid DVR for many reasons, the most significant of which is to utilize existing analog cameras, while adding megapixel cameras to areas that need more detailed monitoring with clear digital zoom-in capabilities. HD cameras can also be used to minimize analog camera count, as they have more pixels and can cover large areas of real estate with a minimal number of cameras.
Analog, a closed-circuit television system (abbreviated by CCTV), is the traditional video signal, which has been in use for decades, and is typically carried over coaxial cable. In some cases people use Cat5 network cable to send video and even audio and power over network cable with the use of baluns, which are adapters that convert the camera’s BNC connector to RJ45 for Cat5, or to twisted pair, which is common for video-only signals. The typical distance limit for coaxial cable is between 250 to 450 feet, depending on the quality of the cable. With baluns and Cat5 cable, this limit can be extended to several miles.
Analog cameras are typically plug-and-play, meaning there is no additional configuration required. Once the camera is plugged into a video and power source, the image is immediately displayed on the screen. The most common resolutions for analog cameras are 352×240 (CIF), 640×480 (VGA), 704×480 (4CIF), and 720×480 (D1). As of 2013 a recent introduction to analog CCTV camera resolution has been 960×480 (960H), which is 33.3% improvement in horizontal pixels.
HD-SDI was introduced after IP cameras began the megapixel revolution for HD video surveillance. HD-SDI is a closed-circuit video signal that delivers at two main resolutions: 720P (1.3-megapixels) and 1080P (2.1-megapixels). An HD-SDI camera cannot be used on a traditional analog DVR. And when not using an HD-DVR, an HD-SDI signal can be converted to HDMI to have the image displayed on an HDTV. The main advantages of HD-SDI over IP cameras are as follows: (1) no brand compatibility issues: simply use your HD-SDI camera with an HD-SDI DVR; (2) no pre-configuration of assigning IP information to a camera; (3) no network bandwidth issues; (4) no latency; and (5) no learning curve.
IP cameras are network based, meaning instead of connecting directly to a DVR (digital video recorder), they connect to the network via a network switch. Older IP cameras required auxillary power, while since 2010 or so the market’s main demand for IP cameras is PoE, or Power over Ethernet. Instead of having to use an auxiliary power source, a PoE IP camera receives power and data over a single Cat5 or Cat6 network cable, which is either connected to a PoE midspan or injector, or to a PoE Switch. A PoE switch is the most common of the three PoE-powered devices, as it is a hub for one or more cameras, as well as the hybrid DVR or NVR (network video recorder) to connect to the same network.
First and foremost when choosing an IP camera (or network camera) and a hybrid DVR or NVR, one must check the compatibility of the recorder’s video management software (VMS) and the camera. If the camera’s make and model is not listed on the VMS’ compatibility list, then that IP camera is most likely not compatible. Incompatible cameras will either not display video, or will not record on one or more streams in motion detection. In recent years, there has been a common standard between IP camera manufacturers called Onvif. If the VMS or recorder is Onvif-compliant, and if the IP camera is Onvif compliant, then the camera is theoretically compatible with the VMS/recorder. However, this comes with certain limitations. Although the video will be displayed on the hybrid DVR or NVR, it is not guaranteed that all of the camera’s features will work. The most common needs for an IP camera, especially if megapixel resolution or higher, is to be able to record on a higher-compressed stream such as H.264, and usually to be able to record on motion detection. Other compatibility issues are IP PTZ (pan-tilt-zoom) cameras, or any IP camera which has the ability to pan, tilt, or zoom. For example, If an IP camera advertises an optical zoom feature, where the lens actually moves to zoom in or out, Onvif compatibility will not offer zoom controls. The same applies to when the IP camera has a fisheye lens and it will be de-warped so as to act like a PTZ camera but without any moving parts. Unless the camera is listed as compatible in the VMS, the fisheye IP camera’s lens cannot be de-warped.
H.264 offers 50% better compression over MPEG-4, and over 80% better compression over MJPEG. (It will reduce the load of the Hybrid DVR or NVR to setup camera-side motion detection, but when working with a lower number of IP cameras, one can opt to control the motion detection from the VMS instead.) After all, when using less data, the entire system will require less storage space to record for the same period of time, and it will require less bandwidth when viewing the cameras from a remote device.
In addition, one must be considerate of the network’s bandwidth limitation when designing a camera system that includes IP cameras. The most common IP cameras on the market as of 2014 are between 1.3MP (720P HD) and 5-megapixels. A 2.1-megapixel (1080P Full HD) IP camera running at real-time 30fps at an uncompressed image stream will typically use 8 Megabits per second (Mbps). Network administrators generally advise for bandwidth consumption not to exceed 80% of the network’s capability, otherwise one will risk cameras being dropped or network hiccups. So for example, if using a 10/100Mbps switch, the total local area network (LAN) bandwidth is 100Mbps. If using 1080P IP cameras at MPEG4 or MJPEG streams at the best image quality at 30fps, with each camera using approximately 8Mbps, the maximum recommended number of 1080P cameras on that network will be 10. To lift that limitation, one can upgrade the PoE switch to Gigabit, or 10/100/1000, and that would increase the maximum number of 1080P cameras to 100.
It is a common practice for hybrid DVRs or NVRs to use a Dual Gigabit NIC (network interface card). This will separate the camera system’s network from the main network, so that the main network’s traffic does not get interrupted by the heavy bandwidth requirements of the camera system’s network. Between Internet browsing, checking email, Voice over IP (VOIP) phones, and other high priority network tasks, it is generally recommended to separate the two networks when the camera’s network will utilize more than 25% of the main network’s capacity.
Most IP cameras require some type of pre-configuration (setting the IP address, subnet mask, gateway, and DNS info) and post-configuration setup (motion detection, alerts, etc.). So between the compatibility checks, pre-configuration, and post-configuration, one may wonder why IP cameras are even a popular choice in the security camera market. The biggest advantages of IP cameras over analog or HD-SDI is the ability to record in higher than 1080P resolution, as well as scalability of the camera system. HD-SDI is currently limited to 720P and 1080P cameras, whereas IP cameras can record in over 40 megapixels, as long as that recording resolution and/or bitrate is supported by the Hybrid DVR or NVR. Regarding system scalability, certain robust NVRs can accommodate hundreds or even over a thousand IP cameras, whereas the analog or HD-SDI systems are typically limited to up to 16, 32, or 64 cameras.
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Raymond Shadman 03/16/2014
Posted In: Video Surveillance