Video decoder

This article is about decoding analog video signals. For digital video compression decoders, seevideo codec.

Integrated circuit video decoder (Philips SAA7114H)

Avideo decoderis anelectronic circuit,often contained within a singleintegrated circuitchip, that converts base-bandanalog videosignals to digital video.Video decoders commonly allow programmable control over video characteristics such ashue,contrast,andsaturation.A video decoder performs the inverse function of avideo encoder,which converts raw (uncompressed) digital video to analog video. Video decoders are commonly used invideo capture devicesandframe grabbers.

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 (compositeorS-Video) that conforms to SD formats such asNTSCorPAL.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-bit4:2:2,12-bit4:1:1,BT.656(SD) orBT.1120(HD). Usually, in addition to the digital video output bus, a video decoder will also generate aclock signaland other signals such as:

• Sync— indicates the beginning of a video frame
• Blanking— indicates video blanking interval
• 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 theanalog signalis digitized by ananalog-to-digital converterto produce a raw, digital data stream. In the case ofcomposite video,theluminanceandchrominanceare then separated; this is not necessary forS-Videosources. 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 acolor spaceconverter to generate data in conformance with any of several color space standards, such asRGBandYCbCr.Together, these steps constitutevideo decodingbecause they "decode" an analog video format such asNTSCorPAL.