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Unit 5: Video

Further confusing things, the non-RGB component cables usually have red, green and blue plugs notes
and jacks, even thought the two methods of signal transfer are not compatible. Lower in quality is
the Y/C signal that makes up separate video (S-Video), an analogue video signal, used in super
VHS and Hi-8 video. As with component video, the Y indicates the brightness (or luminance)
information, but in S-Video colour (or chromonance), information is combined and designated
by C.
The least separation (and thus the lowest quality for a video signal) occurs when all the signals
are mixed together and carried on a single cable as a composite of the three colour channels and
the sync signal; this system yields less-precise colour definition, which cannot be manipulated
or colour corrected as much as an RGB or component signal.
In analogue systems, the video signal from the camera is delivered to the video in connector(s) of
a VCR, where it is recorded on magnetic videotape. A camcorder combines both camera and tape
recorder on a single device. One or two channels of sound may also be recorded on the videotape
(mono or stereo). The video signal is written to tape by a spinning recording head that changes
the local magnetic properties of the tape’s surface in a series of long diagonal stripes.

Since the head is canted or tilted at a slight angle compared with the path of the tape, it follows
a helical (spiral) path, which is called Helical scan recording. As illustrated in Figure 5.1, each
stripe represents information for one field of a video frame. A single video frame is made up of
two fields that are interlaced.

Audio is recorded on a separate straight-line track at the top of the videotape, although with
some recording systems (notably for 3/4 inch tape and for 3/2 inch tape with high-fidelity audio),
sound is recorded helically between the video tracks.
l At the bottom of the tape is a control track containing the pulses used to regulate speed. Tracking
is fine adjustment of the tape so that the tracks are properly aligned as the tape moves across
the playback head. This is how your VCR works.

figure 5.1: video frame

5.2 Broadcast video standards

Most countries around the world use following broadcast standards. These are the main
standards: NTSC, PAL, SECAM, ATSC and DTV. However, each standard is not compatible
with the other.

5.2.1 national television system Committee (ntsC)
Most countries using the NTSC standard, as well as those using other analogue television
standards, are switching to newer DTV standards, of which at least four different ones are in use

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