Download Wires for Video

Wires for Video
There are many different wires for transmitting video and this can be a very confusing topic, so
let?s talk about each of them and give some recommendations on which to use. At the highest
level, there are two types of signals: analog and digital.
Analog Video Signals
There are many types of analog video signals including: RF, Composite, S-Video, Component,
Y/Pr/Pb (a.k.a., YUV, color difference, YPbPr, Y/B-Y/R-Y, and YCbCr.), and RGB (and its two
cousins RGB H/V and RGBHV) - each has its own type of connector. In general, the more
wires the signal uses, the better the signal quality.
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RF is the worst quality of the group. It combines audio and video on the same wire. The
wire is a coax cable and typically uses a screw-on connector called an F connector, but
sometimes uses a BNC connector (see below).
Composite is better than RF. It has one wire just for video (that is, the audio signal is not
carried by the Composite video wire). This wire usually uses RCA connectors (but in
rare cases uses a BNC connector which means you will probably need a BNC-to-RCA
adaptor to connect it to anything else).
S-Video has 2 wires for video ? one for the chrominance (color) and one for the
luminance (brightness) ? thus producing better color saturation and black levels. This
wire uses a round connector with multiple pins inside of it.
Component has 3 wires ? one for luminance (brightness), one for red color information,
and one for blue color information ? thus producing better colors. The Component cable
almost always has 3 RCA connectors. However, sometimes a display will use a 15-pin
D-SUB connector. In this case you will usually need a cable that is 3 RCA connectors
on one side and the 15-pin D-SUB on the other.
Y/Pr/Pb (a.k.a., YUV, color difference, YPbPr, Y/B-Y/R-Y, and YCbCr.) is Component.
They are one and the same. However, you often see the term Y/Pr/Pb used with HDTV
where as you see the term Component used with DVD players. Since Y/Pr/Pb is
Component, it uses the same connectors as Component.
Ultimately, all other signals must end up as RGB to feed the picture tube, plasma or
LCD panel. However, video content (e.g., pictures and movies) are never stored in this
format, so, in reality it is not any better than Component. RGB is available in 4 different
signal/connector types:
 Straight RGB in which the sync signal is embedded in the green signal and the
cable has 3 BNC connectors
 RGB H/V in which the sync signal is on a 4th wire and it has 4 BNC connectors,
 RGBHV in which there are separate horizontal and vertical sync wires for a total
of 5 wires - all of which use BNC connectors, and
 VGA which is equivalent to RGBHV but uses a 15-pin D-SUB connector. This is
by far the most common RGB format as it is the format used to send the video
signal from a computer to the computer's monitor.
RF
BNC
F Connector
S-Video
Composite
Component
Digital Signals
In addition to all of the different types of analog signals, there are four digital signals that
you may see used with video equipment.
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IEEE 1394 Firewire is a relatively old standard that has appeared on some AV
components. A major objection to this standard by the broadcasters is that it
does not inherently include any encryption standard (that is, they cannot prevent
you from copying the digital content).
Digital Video Interface or DVI is a standard for one-way digital communications
from a source to a display. More importantly, the standard includes an encryption
format (High Bandwidth Digital Content Protection or HDCP) that is transmitted
and received by DVI-compliant displays and is used to protect digital content
from being recorded. DVI ports appear on a number of high end video
components.
High-Definition Multimedia Interface or HDMI is a standard that combines DVI
video and multi-channel audio into the same connector. It is relatively new, but is
gaining in popularity with high-end video components.
TCP/IP over Ethernet or WiFi (or perhaps Bluetooth) uses industry-standard
networking protocols to transmit the video signal. This method will become far
more popular as Microsoft Media Center devices begin to take off.
IEEE 1394
Interlaced vs. Progressive
DVI
HDMI
Beyond all of the different wire types for video, there is the issue of how to transmit the
video: progressive scan vs. interlaced. In progressive scanning, the whole frame of the
video signal is scanned onto the display at once. Where as, with interlaced, first the odd
numbered horizontal lines are scanned onto the display and then the even ones are
scanned onto the display. For a given frame rate, progressive is better because it does
not appear to flicker. Computer screens use progressive scan where as traditional
broadcast TVs use interlaced. One more slightly esoteric issue is that when the industry
talks about the interlace rate, they actually talk about the rate of displaying just one half
of the frame, where as, when they talk about the progressive scan rate, they talk about
the rate of displaying the whole frame. This means that the actual frame rate of interlaced
is half its stated rate. Therefore, 1080 interlaced (1080I) puts out 540 lines of resolution
on each refresh, and this is fewer lines per refresh than 720 progressive (720p) which
puts out 720 lines of resolution per refresh. Interlaced can be transmitted over all of the
analog types of wires. Both progressive and interlaced are defined over Component,
RGB, DVI and HDMI. Where as RF, Composite, and S-Video use interlaced.
Interaction of Video Signals
On most AV components the Composite input is disabled when the S-Video input port of
the same input connector group has a connection going to it. For example, if you connect
the Composite output of a VCR to the "Video 1" input of a TV and you connect the SVideo output of the same VCR to the same "Video 1" input of the TV (i.e., the same IR
code is used to select the group of connectors that includes both the Composite and the
S-Video ports), then it is likely that the Composite path will not exist. This can be
important if you try to connect a camera to the Composite input ports on the front of the
VCR because you will not be able to view the camera on the TV until you transfer the
video to a VCR tape and then play it back (note that you may still be able to hear the
audio even though you cannot see the video).
We have also seen a few AV components (such as the EchoStar Dish 501 PVR) where
the Composite output is disabled when the S-Video output is connected to another AV
component. This means that the Composite output cannot be used for Video Sync,
either.
Some AV sources that output a progressive signal, will not output Composite or S-Video
at the same time (because Composite and S-Video are inherently interlaced signals).
This is especially true of satellite receivers and set top boxes, but less often true of DVD
players.
Summary
In summary, to get the highest quality signal, use DVI or HDMI when you can. Otherwise,
use Component. If you are using older AV components such as a VCR, S-Video is likely
to be the highest quality signal you can get. Use 720p if you can, or in decreasing
preference use: 1080i, 480p, or 480i. Note that 480i is the inherent signal quality of a
DVD disk. If you have a separate video processor or one in the display or projector, you
may want to send this signal to it and let the video processor improve the signal.
If you need the signal to run a long way in a distributed video application, you will
probably want to use Composite video because the video signal is all on one wire and
thus does not suffer from skew between different components of the video signal (and it
is much cheaper to run Composite wire). If you want to distribute live TV, recorded TV,
DVD, and/or photographs to PCs and TVs throughout your house using IP over Ethernet
or WiFi, then you may want to check out the Microsoft Media Center architecture for
networked AV content.