What is DVR

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. DVRs have evolved into devices that are feature rich and provide services that exceed the simple recording of video images that was previously done through VCRs. A DVR CCTV system provides a multitude of advanced functions over VCR technology 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.

Security DVRs may be categorized as being either PC based or embedded. A PC based DVRís architecture is a classical personal computer with video capture cards designed to capture video images. An embedded type DVR is specifically designed as a digital video recorder with its operating system and application software contained in firmware or read only memory.

Hardware features

Hardware features of security DVRs vary between manufacturers and may include but are not necessarily limited to

  • Designed for rack mounting or desktop configurations.
  • Single or multiple video inputs with connector types consistent with the analogue or digital video provided such as coaxial cable, twisted pair or optical fiber cable. The most common number of inputs are 1, 2, 4, 8, 16 and 32. Systems may be configured with a very large number of inputs by networking or bussing individual DVRs together.
  • Looping video outputs for each input which duplicates the corresponding input video signal and connector type. These output signals are used by other video equipment such as matrix switchers, multiplexers, and video monitors.
  • Controlled outputs to external video display monitors.
  • Front panel switches and indicators that allow the various features of the machine to be controlled.
  • Network connections consistent with the network type and utilized to control features of the recorder and to send and/or receive video signals.
  • Connections to external control devices such as keyboards.
  • A connection to external pan-tilt-zoom drives that position cameras.
  • Internal CD, DVD, VCR devices typically for archiving video.
  • Connections to external storage media.
  • Alarm event inputs from external security detection devices, usually one per video input.
  • Alarm event outputs from internal detection features such as motion detection or loss of video.

Software features

Software features vary between manufacturers and may include but are not necessarily limited to

  • User selectable image capture rates either on an all input basis or input by input basis. The capture rate feature may be programmed to automatically adjust the capture rate on the occurrence of an external alarm or an internal event
  • Selectable image resolution either on an all input basis or input by input basis. The image resolution feature may be programmed to automatically adjust the image resolution on the occurrence of an external alarm or an internal event.
  • Compression methods determine quality of playback. H.264 hardware compression offers fast transfer rates over the internet with high quality video.
  • Motion detection: Provided on an input by input basis, this feature detects motion detection in the total image or a user definable portion of the image and usually provides sensitivity settings. Detection causes an internal event that may be output to external equipment and/or be used to trigger changes in other internal features.
  • Lack of motion detection. Provided on an input by input basis, this feature detects the movement of an object into the field of view and remaining still for a user definable time. Detection causes an internal event that may be output to external equipment and/or used to trigger changes in other internal features.
  • Direction of motion detection. Provided on an input by input basis, this feature detects the direction of motion in the image that has been determined by the user as an unacceptable occurrence. Detection causes an internal event that may be output to external equipment and/or be used to trigger changes in other internal features.
  • Routing of input video to video monitors based on user inputs or automatically on alarms or events.
  • Input, time and date stamping.
  • Alarm and event logging on appropriate video inputs.
  • Alarm and event search.
  • One or more sound recording channels.
  • Archival.
  • Commercial hopping. Rather than fast-forwarding through commercials, an undocumented feature of the TiVo box is that the user can reprogram the tab-to-end button by entering a sequence of buttons on the remote: SELECT-PLAY-SELECT-3-0-SELECT and listening for the confirming chimes that signal the feature has been activated (or deactivated). The tab-to-end button no longer jumps to the end of a recording when so activated: It skips 30 seconds, which is the length of U.S. commercials. In combination with the 8-second rewind button, most viewers can completely miss commercial breaks in programming.

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