In the context of video acquisition, a video decoder refers to an electronic circuit, often contained within a single integrated circuit chip, that converts base-band analog video signals to digital components video. Video decoders commonly allow programmable control over video characteristics such as hue, contrast, and saturation. A video decoder performs the inverse function of a video encoder, which converts raw (uncompressed) digital video to analog video. Video decoders are commonly used in video capture devices and frame grabbers.
Video decoding involves several processing steps. First, the analog signal is digitized by an analog-to-digital converter to produce a raw, digital data stream. In the case of composite video, the luminance and chrominance are then separated; this is not necessary for S-Video sources. Next, the chrominance is demodulated to produce color difference video data. At this point, the data may be modified so as to adjust brightness, contrast, saturation, and hue. Finally, the data is transformed by a color space converter to generate data in conformance with any of several color space standards, such as RGB and YCbCr. Together, these steps constitute video decoding because they "decode" an analog video format such as NTSC or PAL.
