A decoder is a circuit that changes a code into a set of signals. It is called a decoder because it does the reverse of encoding, but we will begin our study of encoders and decoders with decoders because they are simpler to design.
Video decoders, also known as video servers, enable an existing analog CCTV video surveillance system to be integrated with a network video system. Video decoders play a significant role in installations where many analog cameras are to be maintained.A video decoder makes it possible for an analog CCTV system to migrate to a network video system. It enables users to gain the benefits of network video without having to discard existing analog equipment such as analog CCTV cameras and coaxial cabling.