A video decoder decodes digital video and audio coming from a video encoder or a network camera into analog signals, which can then be used by analog monitors, such as regular TV sets, and video switches. A typical case could be in a retail environment where the user may want to have traditional monitors in public spaces to demonstrate that video surveillance is used.
Another common application for video decoders is to use them in an analog-to-digital-to-analog configuration for transporting video over long distances. The quality of digital video is not affected by the distance traveled, which is not the case when sending analog signals over long distances. The only downside may be some level of latency, from 100 ms to a few seconds, depending on the distance and the quality of the network between the end points.
A video decoder has the ability to decode and display video from many cameras sequentially; that is, decoding and showing video from one camera for some seconds before changing to another and so on.