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{{About|decoding analog video signals|digital video compression decoders|video codec}}
[[File:SAA7114H video decoder by Philips-3610.jpg|thumb|Integrated circuit video decoder (Philips SAA7114H)]]
A '''video decoder''' is an [[electronic circuit]], often contained within a single [[integrated circuit]] chip, that converts base-band [[analog video]] signals to digital video.<ref name=VideoDemystified>{{cite book|last1=Jack|first1=Keith|title=Video demystified : a handbook for the digital engineer|date=1996|publisher=HighText Interactive|location=San Diego, CA|isbn=1-878707-23-X|page=233|edition=2nd}}</ref> Video decoders commonly allow programmable control over video characteristics such as [[hue]], [[contrast (vision)|contrast]], and [[colorfulness|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 device]]s and [[frame grabber]]s.

==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 video|composite]] or [[S-Video]]) that conforms to SD formats such as [[NTSC]] or [[PAL]]. 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]], [[ITU-R BT.656|BT.656]] (SD) or [[BT.1120]] (HD). Usually, in addition to the digital video output bus, a video decoder will also generate a [[clock signal]] and other signals such as:

* [[Frame synchronization (video)|Sync]] — indicates the beginning of a video frame
* [[blanking (video)|Blanking]] — indicates video blanking interval
* [[field (video)|Field]] — 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]] 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]].

==References==

{{reflist}}
{{Electronics-stub}}
[[Category:Electronic circuits]]

Video decoder - Revision history

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