Editing Analog television (section)

===Structure of a video signal===
The video carrier is demodulated to give a [[composite video]] signal{{efn|The RF signal modulation is inverted compared to the conventional AM{{snd}}the minimum video signal level corresponds to maximum carrier amplitude, and vice versa.}} containing luminance, chrominance and synchronization signals.<ref>{{cite web|url=http://www.tek.com/Measurement/App_Notes/25_7075/eng/25W_7075_3.pdf?wt=480&wtwi=2217&wtla=EN&wtty=TI&wtsty=Primer&wtpt=DETAILS&wtlit=25W-7075-3&wtcat=signal+generators&wtti=PAL+Video+Measurements|title=Pal systems&nbsp;– Television measurements|date=September 1999|publisher=Tektronics Incorporated|access-date=25 November 2010|url-status=dead|archive-url=https://web.archive.org/web/20110718081158/http://www.tek.com/Measurement/App_Notes/25_7075/eng/25W_7075_3.pdf?wt=480&wtwi=2217&wtla=EN&wtty=TI&wtsty=Primer&wtpt=DETAILS&wtlit=25W-7075-3&wtcat=signal+generators&wtti=PAL+Video+Measurements|archive-date=18 July 2011}}</ref> The result is identical to the composite video format used by analog video devices such as [[VCRs]] or [[CCTV camera]]s. To ensure good linearity and thus fidelity, consistent with affordable manufacturing costs of [[Television transmitter|transmitters]] and receivers, the video carrier is never modulated to the extent that it is shut off altogether. When intercarrier sound was introduced later in 1948, not completely shutting off the carrier had the side effect of allowing intercarrier sound to be economically implemented.

[[File:Video-line.svg|center|alt=Diagram showing video signal amplitude against time.]]
[[File:NTSC Signal.png|thumb|400px|[[NTSC]] [[composite video]] signal (analog)]]
[[File:An interlaced PAL frame with 20ms duration.jpg|thumb|400px|right|A waterfall display showing a 20&nbsp;ms long interlaced PAL frame with high FFT resolution]]
Each line of the displayed image is transmitted using a signal as shown above. The same basic format (with minor differences mainly related to timing and the encoding of color) is used for PAL, [[NTSC]], and SECAM television systems. A monochrome signal is identical to a color one, with the exception that the elements shown in color in the diagram (the [[colorburst]], and the chrominance signal) are not present.

[[File:Videosignal porch.jpg|right|400px|thumb|Portion of a PAL video signal. From left to right: end of a video [[scan line]], front porch, horizontal [[sync pulse]], back porch with [[colorburst]], and beginning of next line]]
The ''front porch'' is a brief (about 1.5 [[microsecond]]) period inserted between the end of each transmitted line of picture and the leading edge of the next line's [[sync pulse]]. Its purpose was to allow [[voltage]] levels to stabilise in older televisions, preventing interference between picture lines. The ''front porch'' is the first component of the [[horizontal blanking interval]] which also contains the horizontal sync pulse and the ''back porch''.<ref name="tveng" /><ref name="analogtv" /><ref name="Maxim">{{cite web |title=Basics of Analog Video |url=https://www.maximintegrated.com/en/design/technical-documents/tutorials/7/734.html |website=maximintegrated.com |publisher=Maxim |access-date=21 May 2021}}</ref>

The ''back porch'' is the portion of each scan line between the end (rising edge) of the horizontal sync pulse and the start of active video. It is used to restore the black level (300&nbsp;mV) reference in analog video. In signal processing terms, it compensates for the [[fall time]] and [[settling time]] following the sync pulse.<ref name="tveng" /><ref name="analogtv" />

In color television systems such as PAL and NTSC, this period also includes the [[colorburst]] signal. In the SECAM system, it contains the reference subcarrier for each consecutive color difference signal in order to set the zero-color reference.

In some professional systems, particularly [[satellite link]]s between locations, the digital audio is embedded within the line sync pulses of the video signal, to save the cost of renting a second channel. The name for this proprietary system is [[Sound-in-Syncs]].