Watch this video for a more detailed definition of video decoder and how they help with live streaming video applications
A video decoder is a hardware device or software that converts an encoded digital stream into audio, video, closed captions, and subtitles that can be displayed on a television or portable viewing device. Video decoders can be stand-alone devices, server blades, included as part of a set top box, included as a microchip within a viewing device, or as software for a computer.
In terms of functionality, video decoders allow programmable control over a variety of video features, including hue, contrast, and saturation. They receive encoded video input signals that conform to standards formats such as NTSC or PAL. In addition to digital video and output, video decoders can also display EPG data, closed captioning, and subtitles.