[mythtv-users] vga to component converters

[Cory Papenfuss]

On Mon, 26 Sep 2005, Erich Boleyn wrote:

>
> Jason Temple <jason at temple.net> wrote:
>
>>     I was wondering what most of you HD guys use to connect your front
>> end to your tv.  I don't have a fancy flat panel tv with vga imputs
>> unfortunately, but my Samsung tube can do 720p through it's component
>> connector.  I've seen a number of converters anywhere from $150-$300
>> that will take a vga signal and output component...my questions are: Are
>> they any good?  Are there any issues with X (Xorg supports them?  Any
>> issues with modelines, clocks?).  Are they all pretty much the same?
>> Although I'm planning to set this up with 720p, I want it to support
>> 1080i for future sets.  Any input would be greatly apprectiated!
>
> I used to use a tube TV which had Component video inputs (still have it,
> but going to sell it soon when I get my act together) and an Audio
> Authority 9A60.  The TV supported 480i/p and 1080i, though I had a
> bear of a time finding a working mode.
>
> Here's what I did:
>  --  NVidia FX 5200 w/2 outputs, one DVI and one VGA.
>  --  Tube TV is an AdventTV 32" HDTV model.
>  --  Using NVidia proprietary drivers.
>  --  1280x960 32-bit color buffer.
>  --  One putting out 1280x960 @ 75 Hz.
>  --  One putting out 1280x960 interlaced using this modeline:
>        ModeLine "1280x960hdtv" 54.540 1280 1424 1480 1616 960 1016 1032 1124 interlace +hsync +vsync
>
> NOTE:  I first tried a 480p mode with no lasting success (it would glitch
> regularly, looked like a sync issue), and only after some experimentation
> got the 960 interlaced line above working stably.
>
 	Component is almost exactly the same as RGB on a VGA port.  The 
only significant difference is that the color has been transformed into 
YPbPr.  There are a number of schematics and howtos out there on how to 
build your own transcoder.  If you are too lazy to do that, but one for 
$100.

 	Also, resolutions on digital DV are not nearly as wishy-washy and 
ill-defined as for analog NTSC/PAL.

480p :=  720x480   @ 60Hz frame, 60Hz field rate, 31.5kHz Horiz
720p :=  1280x720  @ 60Hz frame, 60Hz field rate, 44.9kHz Horiz
1080i := 1920x1080 @ 30Hz frame, 60Hz field rate, 33.75kHz Horiz

(e.g. http://videosystems.com/mag/video_getting_tune_dtv/)

 	One can quibble about 1080p at 24, 480p at 59.9 Hz, etc, but the above 
are the de-facto definitions.  Why would someone use a 1280x960 modeline 
to output to a HDTV?  It's not a standard size and barely a standard 
frequency.  The computer and/or the HDTV will be doing scaling.

 	Do yourself a favor... read some of the HOWTOs on modeline 
generation (e.g. the one in the mythtv wiki that someone copied from one 
of my previous posts).  Random tweaking of numbers in a modeline is a good 
way to destroy a monitor/tv.

 	In the meantime, may I suggest these as more standard modelines:

Modeline "480i"  14.349 720 760 824 912 480 484 492 525 interlace
Modeline "480p"  28.698 720 760 824 912 480 484 492 525
ModeLine "720p" 74.086 1280 1320 1376 1648 720 722 728 750
ModeLine "1080i" 74.175824 1920 1960 2008 2200 1080 1084 1094 1125 interlace

 	YES they will have overscan... that's how TV works.  Reducing it 
in the horizontal dimension is relatively simple.  Reducing it in the 
vertical dimension violates the standard frequencies or resolutions or 
both.

-Cory

  --

*************************************************************************
* Cory Papenfuss                                                        *
* Electrical Engineering candidate Ph.D. graduate student               *
* Virginia Polytechnic Institute and State University                   *
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