Surveillance is the monitoring of the behavior, activities, or other changing information, usually of people for the purpose of influencing, managing, directing, or protecting them. This includes observation from a distance by means of electronic equipment (such as closed-circuit television (CCTV) cameras)
Closed-circuit television (CCTV) Cameras can produce images or recordings for surveillancepurposes, and can be either video cameras, or digital stills cameras.
Closed-circuit television (CCTV) is the use of video cameras to transmit a signal to a specific place, on a limited set of monitors. It differs from broadcast television in that the signal is not openly transmitted, though it may employ point to point (P2P), point to multipoint, or mesh wireless links. Though almost all video cameras fit this definition, the term is most often applied to those used for surveillance in areas that may need monitoring such as banks, casinos, airports, military installations, and convenience stores. Video-telephony is seldom called “CCTV” but the use of video in distance education, where it is an important tool, is often so called.
In industrial plants, CCTV equipment may be used to observe parts of a process from a central control room, for example when the environment is not suitable for humans. CCTV systems may operate continuously or only as required to monitor a particular event. A more advanced form of CCTV, utilizing digital video recorders (DVRs), provides recording for possibly many years, with a variety of quality and performance options and extra features (such as motion-detection and email alerts). More recently, decentralized IP cameras, some equipped with megapixel sensors, support recording directly to network-attached storage devices, or internal flash for completely stand-alone operation. Surveillance of the public using CCTV is particularly common in many areas around the world.
An analog surveillance camera begins with a CCD sensor and then digitizes the image for processing. But before it can transmit the video, it needs to convert it back to analog so it can be received by an analog device, such as a video monitor or recorder. Unlike IP cameras, analog have no built-in web servers or encoders and require no technical maintenance. These functions are implemented in the recording and/or control equipment.
IP based cameras are the future. They work by turning images and audio into data then transmitting this data over a network or Internet connection. The ultimate benefit of this over analogue CCTV systems is greater flexibility, better performance and easier installation.
Digital Video Recorder
Digital video recorders configured for physical security applications record video signals from closed-circuit television cameras for detection and documentation purposes. Many are designed to record audio as well.
A DVR CCTV system provides a multitude of advanced functions including video searches by event, time, date and camera. There is also much more control over quality and frame rate allowing disk space usage to be optimized and the DVR can also be set to overwrite the oldest security footage should the disk become full. In some DVR security systems remote access to security footage using a PC can also be achieved by connecting the DVR to a LAN network or the Internet. Some of the latest professional digital video recorders include video analytics firmware, to enable functionality such as ‘virtual tripwire’ or even the detection of abandoned objects on the scene.
Network Video Recorder
A network video recorder (NVR) is a software program that records video in a digital format to a disk drive, USB flash drive, SD memory card or other mass storage device. An NVR contains no dedicated video capture hardware. However, the software is typically run on a dedicated device, usually with an embedded operating system. Alternatively, to help support increased functionality and serviceability, standard operating systems are used with standard processors and video management software. An NVR is typically deployed in an IP video surveillance system.
Network video recorders are distinct from digital video recorders (DVR) as their input is from a network rather than a direct connection to a video capture card or tuner. Video on a DVR is encoded and processed at the DVR, while video on an NVR is encoded and processed at the camera, then streamed to the NVR for storage or remote viewing. Additional processing may be done at the NVR, such as further compression or tagging with media data.
Hybrid NVR/DVR surveillance systems exist which incorporate functions of both NVR and DVR; these are considered a form of NVR.
NVR home surveillance systems are generally wireless, tend to be easy to set up, can be accessed through a web browser, and allow the user to be notified by email if an alarm is triggered.
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