Editing Composite video (section)

== Signal components ==
[[File:Composite Video.svg|thumb|right|upright=1.36|Composite video signal graphic]]
[[File:NTSC Signal.png|thumb|[[NTSC]] composite video signal (analog) displayed on a [[Digital storage and sampling oscilloscope|DSO]].]]

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) of the picture and a [[chrominance subcarrier]] which carries the color information (C), a combination of [[hue]] and [[Colorfulness|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 [[harmonic]]s 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 (video)|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]].<ref>{{Cite news |title=Understanding Video Comb Filters |work=Sencore Tech Tips |issue=201 |url=http://www.broadcaststore.com/pdf/model/793698/TT201%20-%204918.pdf}}</ref> 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 {{val|3.58|u=MHz}} burst signal is inverted in phase (180° out of phase) from the reference subcarrier.<ref name="SMPTE 170M-2004">{{cite book |url=https://ieeexplore.ieee.org/document/7291416 |archive-url=https://web.archive.org/web/20180608112731/https://ieeexplore.ieee.org/document/7291416/ |url-status=dead |archive-date=8 June 2018 |title=SMPTE STANDARD for Television – Composite Analog Video Signal – NTSC for Studio Applications |journal=St 170:2004 |date=2004|pages=1–21 |doi=10.5594/SMPTE.ST170.2004 |isbn=978-1-61482-335-3 }}</ref> In PAL, the phase of the {{val|4.43|u=MHz}} color subcarrier alternates on successive lines. In SECAM, no colorburst is used since phase information is irrelevant.

===Composite artifacts===
[[Image:Crawl.jpg|right|thumb|upright=1.36|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 filter]]s 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 physically separate.

=== Recording ===
Most home [[analog video]] equipment record a signal in (roughly) composite format: [[LaserDisc]]s and [[type C videotape]] for example store a true composite signal modulated, while consumer videotape formats (including [[VHS]] and [[Betamax]]) and commercial and industrial tape formats (including [[U-matic]]) use modified composite signals [[FM (modulation)|FM encoded]] (generally known as ''color-under'').<ref>{{cite web|title=US Patent 4323915|url=http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=4323915.PN.&OS=PN/4323915&RS=PN/4323915|publisher=US Patent and Trademark Office|access-date=12 May 2014|url-status=live|archive-url=https://web.archive.org/web/20161220125824/http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=4323915.PN.&OS=PN%2F4323915&RS=PN%2F4323915|archive-date=20 December 2016}}</ref> The professional [[D-2 (video)|D-2]] videocassette format [[digital recording|digitally stores]] a sampled [[analog signal|analog]] composite video signal on [[magnetic tape]]. With the advent of affordable higher sampling speed analog to digital converters, realtime composite to YUV sampled digital sampling has been possible since the 1980s and raw waveform sampling and software decoding since the 2010s.<ref name="CVBS-Decode">{{Cite web |last=Munday |first=Harry |date=2021 |title=CVBS-Decode - Software Defined Composite Video Decoder |url=https://github.com/oyvindln/vhs-decode/wiki/CVBS-Composite-Decode |website=[[GitHub]]}}</ref>

=== 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.