The one technical difficulty rarely addressed in the homebrew
transcoders is the fact that HDTV specifies a differential sync signal.
Regular 480i still uses single-ended (i.e. 'TTL'-like) sync. I think that
480p or higher uses bipolar sync so that it has no net DC value.
Chances are pretty good that a TV will still sync on unipolar
component in. Remember that the sync signal is superimposed on the Y
input. If you get color or brightness weirdness vertically on the TV
after it's all done, it *didn't* have a DC restore circuit. Shouldn't
hurt anything, but the work may be lots of work and not work out.
Building a bipolar sync isn't impossible, but it is more
difficult. To do it right you'd need a PLL circuit to sync to the
unipolar input signal. Since you've got access to the modeline directly,
however, you can likely "advance" the sync pulse so the unipolar sync
triggers the rising edge of the bipolar pulse.
If nothing I said makes sense, just try the HOWTOs as-is...
Report back as to whether it works or not... :)
-Cory
On Mon, 26 Sep 2005, Jason Temple wrote:
Thanks Cory...I'm checking out the howto's now to see if this is indeed the
route I want to go. I'm just looking for 720p for the time being (under the
assumption that if/when someday I get a tv that can take 1080i, it'll have
vga in), so on-the-cheap is important here.
thanks for the help here!
jas
Cory Papenfuss wrote:
On Mon, 26 Sep 2005, Erich Boleyn wrote:
Jason Temple <[EMAIL PROTECTED]> 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 [EMAIL PROTECTED], [EMAIL PROTECTED] 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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* Cory Papenfuss *
* Electrical Engineering candidate Ph.D. graduate student *
* Virginia Polytechnic Institute and State University *
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