OK,
Just to provide a little background info.
There are two common connector formats being used by analog HDTV in the US.
1) High Definition Component
2) RGB
High Definition component is easily confused with standard component video, but HD Component requires much higher signal bandwidth and it's unlikely that a switcher designed for standard definition component will have the required bandwidth to switch HD component without serious degradation of the signal. HD Component uses a video encoding system that encodes the difference between color values. The difference measurement is the parameter being sent through the cable. The connectors used for this connection are typically three separate RCA jacks or maybe three separate BNC jacks, but there may be other connectors that will accept HD component input. More on this a little later.
The second analog video format is RGB. RGB is is exactly the same format used by all VGA video cards and analog monitors. This format mostly uses the standard computer type plug called HD-15. HD-15 is a high density 15 pin connector. You see how creative the engineers are when naming connectors.
http://www.avsforum.com/ubb/wink.gif It's also possible to send VGA across a set of individual cables which is often referred to as 5-BNC. With 5-BNC the cables will be labeled R G B H V. These signals are Red/Green/Blue/Horizontal Sync/Vertical Sync. These same signals are found on the standard HD-15 VGA connector so there is nothing really different about the signal being sent across these cables, just the physical connectors.
Just to confuse things a little more, sometimes computer manufactures produced version of VGA cards that used 4 or even 3 BNC connectors for VGA output. These 4 and 3 BNC systems require that the video signal be modified and the monitor be capable of decoding this special signal. For the most part this was only done with UNIX workstations and some high end PC systems. I'm not aware of any HDTV manufacture who has done this type of thing, so hopefully it's just fading into history as a technical foot note.
The last little confusing tid bit, is that many HDTV's can accept HD component on the HD-15 connector. The TV may automatically detect the proper signal or you may have to manually set this using a set-up menu option. This is a nice feature and if available on your TV should be listed somewhere in the manual.
Here is a brief explanation of HD Component taken from
http://www.crs4.it/~luigi/MPEG/mpeggloss-y.html
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YPbPr
If three components are to be conveyed in three separate channels with identical unity excursions, then the Pb and Pr colour difference components are used:
Pb = (0.5/0.886) * (Bgamma - Y)
Pr = (0.5/0.701) * (Rgamma - Y)
These scale factors limit the excursion of EACH colour difference component to -0.5 .. +0.5 with respect to unity Y excursion: 0.886 is just unity less the luma coefficient of blue. In the analog domain Y is usually 0 mV (black) to 700 mV (white), and Pb and Pr are usually +- 350 mV.
YPbPr is part of the CCIR Rec. 709 HDTV standard, although different luma coefficients are used, and it is denoted E'Pb and E'Pr with subscript arrangement too complicated to be written here.
YPbPr is employed by component analog video equipment such as M-II and BetaCam; Pb and Pr bandwidth is half that of luma.
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The important thing to notice here is that HDTV Component is Y Pr Pb encoding. Standard Component video is Y Cb Cr
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YCbCr
The international standard CCIR-601-1 specifies eight-bit digital coding for component video, with black at luma code 16 and white at luma code 235, and chroma in eight-bit two's complement form centred on 128 with a peak at code 224. This coding has a slightly smaller excursion for luma than for chroma: luma has 219 risers compared to 224 for Cb and Cr. The notation CbCr distinguishes this set from PbPr where the luma and chroma excursions are identical.
For Rec. 601-1 coding in eight bits per component,
Y_8b = 16 + 219 * Y
Cb_8b = 128 + 112 * (0.5/0.886) * (Bgamma - Y)
Cr_8b = 128 + 112 * (0.5/0.701) * (Rgamma - Y)
Some computer applications place black at luma code 0 and white at luma code 255. In this case, the scaling and offsets above can be changed accordingly, although broadcast-quality video requires the accommodation for headroom and footroom provided in the CCIR-601-1 equations.
CCIR-601-1 Rec. calls for two-to-one horizontal subsampling of Cb and Cr, to achieve 2/3 the data rate of RGB with virtually no perceptible penalty. This is denoted 4:2:2. A few digital video systems have utilized horizontal subsampling by a factor of four, denoted 4:1:1. JPEG and MPEG normally subsample Cb and Cr two-to-one horizontally and also two-to-one vertically, to get 1/2 the data rate of RGB. No standard nomenclature has been adopted to describe vertical subsampling. To get good results using subsampling you should not just drop and replicate pixels, but implement proper decimation and interpolation filters.
YCbCr coding is employed by D-1 component digital video equipment.
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RGB is simple in comparison.
When it comes to how to hook everything up, that's particular to the equipment. If your TV can accept both HD component and RGB, that makes things easier. If your TV only accepts Component, then you need the transcoder to convert RGB to HD component if you plan on using a HTPC.
When it comes to switching the signals, I'm not sure there will be an easy to to accomplish this. RGB/VGA switchers are fairly cheap, but generally have HD-15 connectors. The more expensive ones might have 5-BNC, but it's actually preferable to have HD-15 connectors since modern displays use some of the extra pins to communicate display information back to the video card.
What is sounds like here is that you need to switch component signals. Is that right??
Auto switching HD Component signals can be done, but I don't know of any cheap devices that will do it. Cheap meaning something that will not cost more than your TV. One idea is to try using the VGA switcher by taking the component outputs and hooking them up to an old 3-BNC VGA cable. You will need some assorted BNC connectors and maybe a HD-15 gender changer. If it works it should provide a very high quality component video switcher, but it may not work. The problem is that the auto switchers detect the presence of a signal using some information about the RGB signal. Without knowing what pin the switcher is looking at, it may be the case the HD Component will not be detected by the switcher and then it will not automatically switch sources. A manual switcher could still be used and some manual switchers have IR remote controls.
Anyway, there are lots of options it you're willing to experiment a little.
[This message has been edited by JoeFloyd (edited 05-04-2001).]
