DVR (Digital Video Recorder) terminology

A digital video recorder is basically a computer that converts the incoming (analog) signal from the cameras to digital, and compresses it, and stores it. The DVR replaces the function of a multiplexor (or quad or switcher) and a security VCR. There are many advantages of digital video recorders over their analog counterparts.

How do you wish to record and view what the cameras see?

You will need to make a choice between a Time Lapse VCR and a Digital Video Recorder (DVR). Time Lapse VCR's. use videotape to record images at a slower rate of speed than live action. As an example, live action features 30 Frames Per Second (FPS) where as a Time Lapse VCR will record at 20 FPS. Time Lapse VCR's will come in different recording times such as 40 hour, 96 hour, and 168 hour.
DVR's also use time lapse recording but record images onto hard drives like that found in computers. DVR's are more flexible than Time Lapse VCR's because they do not require VHS tapes to be purchased or changed in the machine. Different sized hard drives can yield a much higher storage capacity than a VCR. It is possible to instantly search by date, time or event. There is no signal or quality loss while recording because the recording is digital. You have more flexible configurations and settings and it may be possible depending on the model to remotely view and control your system via the Internet. All of these features however come at a significantly higher cost.


Alarm activated

A DVR that is triggered to start recording from the idle position. If the DVR has pre and post alarm recording then it will be possible to view before and after the event.

Attenuation

Term used to describe the amount of loss seen in a video signal when transmitted from one point to another.

Composite Video

The combination of all electronic information required to produce a video signal. Comprising 0.7 volts video and 0.3 volts sync., hence the term one
volt peak to peak.

Duplex

A duplex device can transmit data into and out of the electronic device at the same time. For example, a full duplex digital video recorder can continue capturing and recording images even while a different image is being displayed.

FPS - Frames Per Second

 Frames Per Second in digital video applications, refers to the number of video images that can be captured, displayed, or recorded in a second. Also referred to as the 'frame rate' or 'refresh rate'.

JPEG

Pronounced "jay-peg" and stands for "Joint Photographic Experts Group" who designed the standard. This is a standard way of compressing images which works particularily well for photographic images (as opposed to graphic art).

Looping

A piece of video equipment that allows video signals to pass through without being terminated.

MPEG

Pronounced "em-peg" and stands for "Motion Picture Experts Group" who designed the standard. This is a standard way of compressing audio and video files. (It's also the technology behind the now world-famous MP3 music files.)

Motion Detection

Refers to the feature in some DVRs to only record video if something in the image moves or changes. Therefore you don't have to look through hours of stored video looking for something to happen. It also saves a lot of space on the hard drive.

PIP - Picture in Picture

Picture in Picture - device used to superimpose one video signal over another in one display.

PTZ - Pan Tilt Zoom

PTZ cameras allow you to adjust the position ('pan' is side-to-side, 'tilt' is up-and-down) and focus ('zoom') of the camera using a remote controller. Due to this added functionality, these cameras tend to cost much more than non-PTZ cameras

Resolution

Refers to how much detail can be captured on a camera or displayed on a monitor. Cameras typically capture about 380 horizontal lines of resolution. High resolution cameras may capture 450 lines of resolution or more. The higher the resolution, the more detail that can be captured in a picture. The monitors and recording devices can generally handle at least as much resolution as the cameras can capture.

Switch / Sequence

A switch will take multiple camera inputs and will show them on the monitor one at a time. Unlike a quad it will not display them all at once, instead it sequences through them showing one camera at a time. It will also allow you to select a particular camera to view.

Simplex

With a simplex multiplexer you can only perform one function of recording or playing back at a time, ie. if you are reviewing images from DVR, you cannot record images or view live images in a multiscreen format

Video Signals

NTSC National Television Standards Committee. Colour Video Signal, North American  and Japanese television standard - 525 Lines, 60Hz.

PAL Phase Alternate Line ­ Colour Video Signal standard for most of Europe,  Australia and the Middle East - 625 Lines, 50Hz.

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