AW: [mythtv-users] Hardware for Best TV-Out?

Joe Votour joevph at
Tue Oct 26 16:22:48 UTC 2004


640x480 should be a good enough resolution.  Mainly,
if I was to use such a circuit (though I'd have to
find somebody who makes them, at the moment, I'm
incapable of making such a beat myself), it would have
to support a mode line that the MythTV GUI doesn't
require jumping through hoops to support (by changing
either the over/underscan or the GUI position).

Perhaps jitter is an incorrect word, I'm not sure, but
here's the basic idea.  Watch CNN or Fox News, the
Business section of the news, or even ESPN on some
sporting events, and they have this little "ticker" -
a scrolling message where text comes from the right
hand side of the screen and scrolls off the left.  It
was a very popular item in old school C64, Amiga and
PC demos as well.

Anyway (possibly long and unnecessary explanation
aside), on a TV, that scrolling message is perfectly
smooth going across.  On my MythTV system (and even a
Windows system running SageTV), the message will have
bursts of smoothness, but will suddenly jump to the
left for a second, and then jump back to the right,
almost as if the ordering of the frames is wrong.

I've read in the mailing list archives that it might
be a PVR-250 problem, so I'll be swapping them out for
a software-based encoder (BT878) when I get a chance,
just to confirm or deny the PVR-250 problem.

When I use my XBox as a frontend, the ticker is very
smooth, which could be due to the Conexant 25871 chip
in it (which is basically an RGB to NTSC chip, or at
least that's one of it's functions).  It also works
with my PVR-350, but there's some major issues
associated with that (as I have documented in other
posts).  Unfortunately, the XBox makes more noise than
my backend PC, and I'm not really keen on swapping
fans, etc. in my XBox.

So, if this circuit works, and if I could find
somebody who could build me one and sell it, I'd
gladly fork over some money.

-- Joe

--- Cory Papenfuss <papenfuss at> wrote:

>  	Aside from VSYNC tearing necessitating
> deinterlacing, the system 
> is brain-dead stupid.  There's no scaling, flicker
> filtering, 
> deinterlacing (on the vid card), etc, etc.  The
> PVR-250 captures 
> interlaced MPEG, and sends it out the VGA port
> interlaced.  When you say, 
> "jitter," do you mean flicker?  I've never paid that
> much attention to 
> ticker scrollers, but I'll look.  Keep in mind that
> there is no way to get 
> rid of flicker on a 480i signal without essentially
> lowpass filtering the 
> signal.  480i is 30Hz, so flicker is part of the
> deal.
>  	The settings I use for X are a custom modeline to
> generate 480i 
> timings.  The actual resolution could be lots of
> things, so long as:
> 1. There are a total of 525 pixels vertically.
> 2. The total time to draw a single horizonal
> scanline is 15.734kHz
> 3. The signal is interlaced.
>  	Other than that, the sky's the limit.  Of course,
> trying to see 
> any more than 480 vertical pixels will be off the
> screen at the 
> top/bottom.  I have made NTSC modelines for 480x480,
> 640x480, 720x480, and 
> 1440x480... they're all fine.  Of course things that
> don't do aspect ratio 
> correction look a bit skinny at 1440x480, but that's
> another issue.
> -Cory
> * Cory Papenfuss							*
> * Electrical Engineering candidate Ph.D. graduate
> student               *
> * Virginia Polytechnic Institute and State
> University 			*
> On Mon, 25 Oct 2004, Joe Votour wrote:
> > Cory,
> >
> > With such a converter, are you able to pass what I
> > call the "CNN test"?  That is, tune to CNN (or
> some
> > other channel with a scrolling ticker), and the
> ticker
> > is completely jitter free (as on a real TV)?
> >
> > Also, what kind of settings do you use for X?  Do
> you
> > run at a "standard" mode of 640x480 or 800x600. or
> do
> > you have to run at a different mode that might not
> > play nicely with the MythTV GUI (for example on
> the
> > PVR-350 output, which is 720x480, the GUI has to
> be
> > resized, and overscan applied to the OSD, which
> has
> > it's own set of problems).
> >
> > -- Joe
> >
> > _______________________________________________
> mythtv-users mailing list
> mythtv-users at

Do you Yahoo!?
Yahoo! Mail Address AutoComplete - You start. We finish. 

More information about the mythtv-users mailing list