Video motion detection (VMD) is a way of defining activity in a scene by analyzing image data and differences in a series of images. The functionality can either be built-in into a network video product or made available with video management software. In-picture alarm programming allows you to define areas of a screen where you want to detect any visual changes.
VMD in DVR (digital video
In such a system, cameras are connected to a DVR, which performs the VMD on each video stream. This allows the DVR to decrease the amount of recorded video, to prioritize recordings and to use motion in a specific area of the image as a search term when searching for events. The downside of this method is that performing VMD is a CPU intensive process and performing VMD on many channels puts a heavy strain on the DVR system.
VMD in network video systems
VMD, as an integrated function of network cameras or video servers, offers substantial advantages over the scenario mentioned above – the most significant being that the VMD is processed in the network camera or video server itself. See event handling in a video server.
Above: System overview
Below: A network camera with built-in VMD feature
This alleviates the workload for any recording devices in the system and makes "event-driven surveillance" possible; that is, unless activity is detected in the scene, no video (or only video with low frame rate) is sent to the operator or recording system. If motion is detected, you may request a number of things to be done automatically; e.g. save images before, during and after the event (called pre- and post-alarm image buffering), start sending images for recording at specified destinations, send alerts to specific individuals via e-mail or SMS to a mobile telephone, activate lights, turn alarm on or off, open or lock doors, control temperature levels etc.
VMD data with information about the activity can also be included in the video stream to simplify activity searches in recorded material.
VMD can also reside in the video management software, thus providing VMD functionality to network cameras that do not originally embed this feature.
Sample of the motion detection user interface offered in AXIS Camera Station software. More samples.
Advantages of local VMD in the "endpoint" (network camera and video server
compared with systems using central analyzing such as DVRs)
Reduces CPU load on recording server
Saves storage space
The camera can interact with others systems using I/O Ports (for example triggering alarms)
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