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 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 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
- 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
- Compression methods determine quality of playback. H.264 hardware
compression offers fast transfer rates over the internet with high quality
- 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
- 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.
- 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