A video decoder is an

electronic circuit An electronic circuit is composed of individual electronic components, such as resistors, transistors, capacitors, inductors and diodes, connected by conductive wires or traces through which electric current can flow. It is a type of electric ...

, often contained within a single

integrated circuit An integrated circuit or monolithic integrated circuit (also referred to as an IC, a chip, or a microchip) is a set of electronic circuits on one small flat piece (or "chip") of semiconductor material, usually silicon. Large numbers of tiny ...

chip, that converts base-band

analog video Video is an electronic medium for the recording, copying, playback, broadcasting, and display of moving visual media. Video was first developed for mechanical television systems, which were quickly replaced by cathode-ray tube (CRT) syste ...

signals to digital video. Video decoders commonly allow programmable control over video characteristics such as

hue In color theory, hue is one of the main properties (called color appearance parameters) of a color, defined technically in the CIECAM02 model as "the degree to which a stimulus can be described as similar to or different from stimuli th ...

, contrast, and

saturation Saturation, saturated, unsaturation or unsaturated may refer to: Chemistry * Saturation, a property of organic compounds referring to carbon-carbon bonds **Saturated and unsaturated compounds ** Degree of unsaturation **Saturated fat or fatty aci ...

. 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 grabber A frame grabber is an electronic device that captures (i.e., "grabs") individual, digital still frames from an analog video signal or a digital video stream. It is usually employed as a component of a computer vision system, in which video frames ...

Signals

The input signal to a video decoder is analog video that conforms to a standard format. For example, a standard definition (SD) decoder accepts ( composite or

S-Video S-Video (also known as separate video, Y/C, and erroneously Super-Video ) is an analog video signal format that carries standard-definition video, typically at 525 lines or 625 lines. It encodes video luma and chrominance on two separate chan ...

) that conforms to SD formats such as

NTSC The first American standard for analog television broadcast was developed by National Television System Committee (NTSC)National Television System Committee (1951–1953), Report and Reports of Panel No. 11, 11-A, 12–19, with Some supplement ...

PAL Phase Alternating Line (PAL) is a colour encoding system for analogue television. It was one of three major analogue colour television standards, the others being NTSC and SECAM. In most countries it was broadcast at 625 lines, 50 fields ( ...

. High definition (HD) decoders accept analog HD formats such as AHD, HD-TVI, or HD-CVI. The output digital video may be formatted in various ways, such as 8-bit or 16-bit 4:2:2, 12-bit 4:1:1, BT.656 (SD) or

BT.1120 BT.1120 is a digital interface standard for HDTV studio signals published by the International Telecommunication Union The International Telecommunication Union is a specialized agency of the United Nations responsible for many matters rel ...

(HD). Usually, in addition to the digital video output bus, a video decoder will also generate a

clock signal In electronics and especially synchronous digital circuits, a clock signal (historically also known as ''logic beat'') oscillates between a high and a low state and is used like a metronome to coordinate actions of digital circuits. A clock sign ...

and other signals such as: * Sync — indicates the beginning of a video frame * Blanking — indicates video blanking interval *

Field Field may refer to: Expanses of open ground * Field (agriculture), an area of land used for agricultural purposes * Airfield, an aerodrome that lacks the infrastructure of an airport * Battlefield * Lawn, an area of mowed grass * Meadow, a grass ...

— indicates whether the current video field is even or odd (applies to interlaced formats) * Lock — indicates the decoder has detected and is locked (synchronized) to a valid analog input video signal

Functional blocks

The main functional blocks of a video decoder typically include these: * Analog processors * Y/C (luminance/chrominance) separation * Chrominance processor * Luminance processor * Clock/timing processor * A/D converters for Y/C * Output formatter * Host communication interface

Process

Video decoding involves several processing steps. First the

analog signal An analog signal or analogue signal (see spelling differences) is any continuous signal representing some other quantity, i.e., ''analogous'' to another quantity. For example, in an analog audio signal, the instantaneous signal voltage varies c ...

is digitized by an

analog-to-digital converter In electronics, an analog-to-digital converter (ADC, A/D, or A-to-D) is a system that converts an analog signal, such as a sound picked up by a microphone or light entering a digital camera, into a digital signal. An ADC may also provid ...

to produce a raw, digital data stream. In the case of

composite video Composite video is an analog video signal format that carries standard-definition video (typically at 525 lines or 625 lines) as a single channel. Video information is encoded on one channel, unlike the higher-quality S-Video (two chann ...

, the

luminance Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted from, or is reflected from a particular area, and falls with ...

and

chrominance Chrominance (''chroma'' or ''C'' for short) is the signal used in video systems to convey the color information of the picture (see YUV color model), separately from the accompanying luma signal (or Y' for short). Chrominance is usually represen ...

are then separated; this is not necessary for

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 The RGB color model is an additive color model in which the red, green and blue primary colors of light are added together in various ways to reproduce a broad array of colors. The name of the model comes from the initials of the three additi ...

and

YCbCr YCbCr, Y′CbCr, or Y Pb/Cb Pr/Cr, also written as YCBCR or Y′CBCR, is a family of color spaces used as a part of the color image pipeline in video and digital photography systems. Y′ is the luma component and CB and CR are the blue-dif ...

. Together, these steps constitute ''video decoding'' because they "decode" an analog video format such as

References

{{Electronics-stub Electronic circuits