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 channels) and the even higher-quality component video (three or more channels). In all of these video formats, audio is carried on a separate connection.
Composite video baseband signal
On consumer products a yellow RCA connector is typically used for composite video.
Composite video is also known by the initials CVBS for composite video baseband signal or color, video, blanking and sync,[4][5] or is simply referred to as SD video for the standard-definition television signal it conveys.
There are three dominant variants of composite video signals, corresponding to the analog color system used: NTSC, PAL, and SECAM. Usually composite video is carried by a yellow RCA connector, but other connections are used in professional settings, or on devices that are too small for an RCA connector, such as a digital camera.
A composite video signal combines, on one wire, the video information required to recreate a color picture, as well as line and frame synchronization pulses. The color video signal is a linear combination of the luminance () of the picture and a modulated subcarrier which carries the chrominance or color information (), a combination of hue and saturation. Details of the combining process vary between the NTSC, PAL and SECAM systems.
The frequency spectrum of the modulated color signal overlaps that of the baseband signal, and separation relies on the fact that frequency components of the baseband signal tend to be near harmonics of the horizontal scanning rate, while the color carrier is selected to be an odd multiple of half the horizontal scanning rate; this produces a modulated color signal that consists mainly of harmonic frequencies that fall between the harmonics in the baseband luma signal, rather than both being in separate continuous frequency bands alongside each other in the frequency domain. The signals may be separated using a comb filter.[6] In other words, the combination of luma and chrominance is indeed a frequency-division technique, but it is much more complex than typical frequency-division multiplexing systems like the one used to multiplex analog radio stations on both the AM and FM bands.
A gated and filtered signal derived from the color subcarrier, called the burst or colorburst, is added to the horizontal blanking interval of each line (excluding lines in the vertical sync interval) as a synchronizing signal and amplitude reference for the chrominance signals. In NTSC composite video, the burst signal is inverted in phase (180° out of phase) from the reference subcarrier.[7] In PAL, the phase of the color subcarrier alternates on successive lines. In SECAM, no colorburst is used since phase information is irrelevant.
Composite artifacts
Enlarged detail from a video source exhibiting dot crawl. Note the distinctive checkerboard pattern on the vertical edges between yellow and blue areas.
The combining of component signals to form the composite signal does the same, causing a checkerboard video artifact known as dot crawl. Dot crawl is a defect that results from crosstalk due to the intermodulation of the chrominance and luminance components of the signal. This is usually seen when chrominance is transmitted with high bandwidth, and its spectrum reaches into the band of the luminance frequencies. Comb filters are commonly used to separate signals and eliminate these artifacts from composite sources. S-Video and component video avoid this problem as they maintain the component signals separately.
Recording
Most home analog video equipment record a signal in (roughly) composite format: LaserDiscs store a true composite signal, while consumer videotape formats (including VHS and Betamax) and commercial and industrial tape formats (including U-matic) use modified composite signals (generally known as color-under).[8] The professional D-2 videocassette format digitally records and reproduces composite video signals using PCM encoding of the analog signal on the magnetic tape.
Extensions
A number of so-called extensions to the visible TV image can be transmitted using composite video. Since TV screens hide the vertical blanking interval of a composite video signal, these take advantage of the unseen parts of the signal. Examples of extensions include teletext, closed captioning, information regarding the show title, a set of reference colors that allows TV sets to automatically correct NTSC hue maladjustments, widescreen signaling (WSS) for switching between 4:3 and 16:9 display formats, etc.
Connectors and cable
Rear of the Polish Elwro 800 Junior computer. DIN output carries a composite video signal to an external monitor.[9]
Intergraph Intense3D Voodoo Rush with TV-out; S-video (topmost connector) and composite video (yellow RCA connector below)
In home applications, the composite video signal is typically connected using an RCA connector, normally yellow. It is often accompanied with red and white connectors for right and left audio channels respectively. BNC connectors and higher quality coaxial cable are often used in professional television studios and post-production applications. BNC connectors were also used for composite video connections on early home VCRs, often accompanied by either RCA connector or a 5-pin DIN connector for audio. The BNC connector, in turn, post dated the PL-259 connector featured on first-generation VCRs.
Video cables are 75 ohm impedance, low in capacitance. Typical values run from 52 pF/m for an HDPE-foamed dielectric precision video cable to 69 pF/m for a solid PE dielectric cable.[10]
Modulators
Some devices that connect to a TV, such as VCRs, older video game consoles and home computers, output a composite signal. This may then be converted to RF with an external box known as an RF modulator that generates the proper carrier (often for channel 3 or 4 in North America, channel 36 in Europe). Sometimes this modulator was built into the product (such as video game consoles, VCRs, or the Atari, Commodore 64, or TRS-80 CoCo home-computers) and sometimes it was an external unit powered by the computer (in the case of the TI-99/4A or some Apple modulators) or with an independent power supply.[a]
Because of the digital television transition most TV sets sold these days no longer have analog television tuners and cannot accept a signal from an analog modulator. But because composite video has a well-established market for both devices that convert it to channel 3/4 outputs, as well as devices that convert things like VGA to composite, it has offered opportunities to repurpose older composite monitors for newer devices.
Demodulation loss
The process of modulating RF with the original video signal, and then demodulating the original signal again in the TV, introduces losses including added noise or interference. For these reasons, it is best to use composite connections instead of RF connections if possible. Older video equipment and some very low-end modern televisions have only RF input (essentially the antenna jack). While RF modulators are no longer common, they are still available to translate composite signals for older equipment.
^In the United States, using an external RF modulator frees the manufacturer from obtaining FCC approval for each variation of a device. Through the early 1980s, electronics that output a television channel signal were required to meet the same shielding requirements as broadcast television equipment, thus forcing manufacturers such as Apple to omit an RF modulator, and Texas Instruments to have their RF modulator as an external unit, which they had certified by the FCC without mentioning they were planning to sell it with a computer. In Europe, while most countries used the same broadcast standard, there were different modulation standards (PAL-G versus PAL-I, for example), and using an external modulator allowed manufacturers to make a single product and easily sell it to different countries by changing the modulator.
References
^"Definition: composite video". computer language. Retrieved 23 May 2019.
^Robert Silva (8 November 2017). "Composite Video - The Basics". Lifewire. Retrieved 14 July 2018.
^"Understanding Video Comb Filters" (PDF). Retrieved 29 May 2020.
^SMPTE STANDARD for Television – Composite Analog Video Signal – NTSC for Studio Applications. 2004.
^"US Patent 4323915". US Patent and Trademark Office. from the original on 20 December 2016. Retrieved 12 May 2014.
^"Elwro 800 Junior - MCbx". oldcomputer.info. from the original on 18 March 2017. Retrieved 5 May 2018.
^"LC-1 Audio Cable Design Notes". Blue Jeans Cable. from the original on 28 November 2011. Retrieved 21 January 2012.
External links
Maxim - Apr 17, 2001 - Video Basics Tutorial covering CVBS format structure.
Marshall Brain (26 November 2006). "Composite Video Signal". Retrieved 1 May 2020.
May 20, 2023
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Not to be confused with Component 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 channels and the even higher quality component video three or more channels In all of these video formats audio is carried on a separate connection Composite video baseband signalOn consumer products a yellow RCA connector is typically used for composite video TypeAnalog video connectorProduction historyDesigned1954 1 1956 2 General specificationsLengthMaximum of 50 m citation needed ExternalYesVideo signalNTSC PAL or SECAM videoPins1 plus grounding shieldConnectorRCA connectorElectricalSignal1 volt 3 PinoutPin 1centervideoPin 2sheathgroundComposite video is also known by the initials CVBS for composite video baseband signal or color video blanking and sync 4 5 or is simply referred to as SD video for the standard definition television signal it conveys There are three dominant variants of composite video signals corresponding to the analog color system used NTSC PAL and SECAM Usually composite video is carried by a yellow RCA connector but other connections are used in professional settings or on devices that are too small for an RCA connector such as a digital camera Contents 1 Signal components 1 1 Composite artifacts 1 2 Recording 1 3 Extensions 2 Connectors and cable 3 Modulators 3 1 Demodulation loss 4 See also 5 Notes 6 References 7 External linksSignal components Edit NTSC composite video signal analog A composite video signal combines on one wire the video information required to recreate a color picture as well as line and frame synchronization pulses The color video signal is a linear combination of the luminance Y displaystyle Y of the picture and a modulated subcarrier which carries the chrominance or color information C displaystyle C a combination of hue and saturation Details of the combining process vary between the NTSC PAL and SECAM systems The frequency spectrum of the modulated color signal overlaps that of the baseband signal and separation relies on the fact that frequency components of the baseband signal tend to be near harmonics of the horizontal scanning rate while the color carrier is selected to be an odd multiple of half the horizontal scanning rate this produces a modulated color signal that consists mainly of harmonic frequencies that fall between the harmonics in the baseband luma signal rather than both being in separate continuous frequency bands alongside each other in the frequency domain The signals may be separated using a comb filter 6 In other words the combination of luma and chrominance is indeed a frequency division technique but it is much more complex than typical frequency division multiplexing systems like the one used to multiplex analog radio stations on both the AM and FM bands A gated and filtered signal derived from the color subcarrier called the burst or colorburst is added to the horizontal blanking interval of each line excluding lines in the vertical sync interval as a synchronizing signal and amplitude reference for the chrominance signals In NTSC composite video the burst signal is inverted in phase 180 out of phase from the reference subcarrier 7 In PAL the phase of the color subcarrier alternates on successive lines In SECAM no colorburst is used since phase information is irrelevant Composite artifacts Edit Enlarged detail from a video source exhibiting dot crawl Note the distinctive checkerboard pattern on the vertical edges between yellow and blue areas The combining of component signals to form the composite signal does the same causing a checkerboard video artifact known as dot crawl Dot crawl is a defect that results from crosstalk due to the intermodulation of the chrominance and luminance components of the signal This is usually seen when chrominance is transmitted with high bandwidth and its spectrum reaches into the band of the luminance frequencies Comb filters are commonly used to separate signals and eliminate these artifacts from composite sources S Video and component video avoid this problem as they maintain the component signals separately Recording Edit Most home analog video equipment record a signal in roughly composite format LaserDiscs store a true composite signal while consumer videotape formats including VHS and Betamax and commercial and industrial tape formats including U matic use modified composite signals generally known as color under 8 The professional D 2 videocassette format digitally records and reproduces composite video signals using PCM encoding of the analog signal on the magnetic tape Extensions Edit A number of so called extensions to the visible TV image can be transmitted using composite video Since TV screens hide the vertical blanking interval of a composite video signal these take advantage of the unseen parts of the signal Examples of extensions include teletext closed captioning information regarding the show title a set of reference colors that allows TV sets to automatically correct NTSC hue maladjustments widescreen signaling WSS for switching between 4 3 and 16 9 display formats etc Connectors and cable Edit Rear of the Polish Elwro 800 Junior computer DIN output carries a composite video signal to an external monitor 9 Intergraph Intense3D Voodoo Rush with TV out S video topmost connector and composite video yellow RCA connector below In home applications the composite video signal is typically connected using an RCA connector normally yellow It is often accompanied with red and white connectors for right and left audio channels respectively BNC connectors and higher quality coaxial cable are often used in professional television studios and post production applications BNC connectors were also used for composite video connections on early home VCRs often accompanied by either RCA connector or a 5 pin DIN connector for audio The BNC connector in turn post dated the PL 259 connector featured on first generation VCRs Video cables are 75 ohm impedance low in capacitance Typical values run from 52 pF m for an HDPE foamed dielectric precision video cable to 69 pF m for a solid PE dielectric cable 10 Modulators EditSome devices that connect to a TV such as VCRs older video game consoles and home computers output a composite signal This may then be converted to RF with an external box known as an RF modulator that generates the proper carrier often for channel 3 or 4 in North America channel 36 in Europe Sometimes this modulator was built into the product such as video game consoles VCRs or the Atari Commodore 64 or TRS 80 CoCo home computers and sometimes it was an external unit powered by the computer in the case of the TI 99 4A or some Apple modulators or with an independent power supply a Because of the digital television transition most TV sets sold these days no longer have analog television tuners and cannot accept a signal from an analog modulator But because composite video has a well established market for both devices that convert it to channel 3 4 outputs as well as devices that convert things like VGA to composite it has offered opportunities to repurpose older composite monitors for newer devices Demodulation loss Edit The process of modulating RF with the original video signal and then demodulating the original signal again in the TV introduces losses including added noise or interference For these reasons it is best to use composite connections instead of RF connections if possible Older video equipment and some very low end modern televisions have only RF input essentially the antenna jack While RF modulators are no longer common they are still available to translate composite signals for older equipment See also EditList of video connectors NTSC color encoding PAL color encodingNotes Edit In the United States using an external RF modulator frees the manufacturer from obtaining FCC approval for each variation of a device Through the early 1980s electronics that output a television channel signal were required to meet the same shielding requirements as broadcast television equipment thus forcing manufacturers such as Apple to omit an RF modulator and Texas Instruments to have their RF modulator as an external unit which they had certified by the FCC without mentioning they were planning to sell it with a computer In Europe while most countries used the same broadcast standard there were different modulation standards PAL G versus PAL I for example and using an external modulator allowed manufacturers to make a single product and easily sell it to different countries by changing the modulator References Edit Definition composite video computer language Retrieved 23 May 2019 the cable bible Retrieved 23 May 2019 Understanding Analog Video Signals Analog Devices Video Basics Maxim Integrated Retrieved 14 July 2018 Robert Silva 8 November 2017 Composite Video The Basics Lifewire Retrieved 14 July 2018 Understanding Video Comb Filters PDF Retrieved 29 May 2020 SMPTE STANDARD for Television Composite Analog Video Signal NTSC for Studio Applications 2004 US Patent 4323915 US Patent and Trademark Office Archived from the original on 20 December 2016 Retrieved 12 May 2014 Elwro 800 Junior MCbx oldcomputer info Archived from the original on 18 March 2017 Retrieved 5 May 2018 LC 1 Audio Cable Design Notes Blue Jeans Cable Archived from the original on 28 November 2011 Retrieved 21 January 2012 External links EditMaxim Apr 17 2001 Video Basics Tutorial covering CVBS format structure Marshall Brain 26 November 2006 Composite Video Signal Retrieved 1 May 2020 Retrieved from https en wikipedia org w index php title Composite video amp oldid 1147380950, wikipedia, wiki, book, books, library,
