[mythtv] VGA to NTSC scan converter
Chris Kleeschulte
mythtv-dev@snowman.net
Thu, 14 Nov 2002 19:47:06 -0700
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well....the scan converter will convert whatever input vert refresh rate =
to 60Hz...my scan converter will take an input of up to 87Hz, but i =
don't get much of difference when changing the vert refresh rate of my X =
session. The real problem is keeping the frames sync'ed in a 1->2 =
pattern....we would like 1 frame per 2 refreshes of the screen (even if =
it is interlaced). We know NTSC vert refresh of 59.94Hz (interlaced) is =
set in stone for regular tv's, so the trick is to sync a frame rate at =
half that (29.97fps) and keep this all sync'ed up. But since we are =
dealing with X11 and the normal linux kernel considers this a normally =
scheduled program (which is subject to a scheduling margin of time), =
myth can become slightly desync'ed causing choppy video (noticeable on =
ticker tapes). This problem would affect any myth users (not just scan =
converter users)....raising the vert refresh rate (like watching tv on a =
computer monitor or through an expensive projector) will buffer this =
problem. something to think about.
Chris
----- Original Message -----=20
From: Broc Stirton=20
To: mythtv-dev@snowman.net=20
Sent: Thursday, November 14, 2002 6:06 PM
Subject: RE: [mythtv] VGA to NTSC scan converter
On Thu, 14 Nov 2002, Jeremy Oddo wrote:
> >
> > Does any one have any info on what refresh would
> > theoretically work best with a scan converter? My first instinct =
(60Hz)
> > proved to most defintely not be the best looking.
> >
> Seriously? I would have guessed 60Hz as well, seeing as how NTSC
> refreshes each field at 60Hz (well, 59.94Hz) I would have guessed =
that
> refreshing faster wouldn't make a difference. Interesting indeed. =
Of
> course, PAL refresh is 50Hz.
>
That was my reasoning (I live in Texas, so NTSC here), but the 60Hz
modelines for 800x600 and 640x480 looked pretty bad. IIRC, it was =
more
flickery. My unit has a flicker filter (not sure how good), but maybe =
the
small diff between the NTSC 59.9xx sync and 60Hz is the problem =
(?)....
_______________________________________________
mythtv-dev mailing list
mythtv-dev@snowman.net
http://www.snowman.net/mailman/listinfo/mythtv-dev
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<BODY bgColor=3D#ffffff>
<DIV><FONT face=3DVerdana size=3D2>well....the scan converter will =
convert whatever=20
input vert refresh rate to 60Hz...my scan converter will take an input =
of up to=20
87Hz, but i don't get much of difference when changing the vert refresh =
rate of=20
my X session. The real problem is keeping the frames sync'ed in a =
1->2=20
pattern....we would like 1 frame per 2 refreshes of the screen =
(even=20
if it is interlaced). We know NTSC vert refresh of 59.94Hz (interlaced) =
is set=20
in stone for regular tv's, so the trick is to sync a frame rate at half =
that=20
(29.97fps) and keep this all sync'ed up. But since we are dealing with =
X11 and=20
the normal linux kernel considers this a normally scheduled program =
(which is=20
subject to a scheduling margin of time), myth can become slightly =
desync'ed=20
causing choppy video (noticeable on ticker tapes). This problem would =
affect any=20
myth users (not just scan converter users)....raising the vert refresh =
rate=20
(like watching tv on a computer monitor or through an expensive =
projector) will=20
buffer this problem. something to think about.</FONT></DIV>
<DIV><FONT face=3DVerdana size=3D2></FONT> </DIV>
<DIV><FONT face=3DVerdana size=3D2></FONT> </DIV>
<DIV><FONT face=3DVerdana size=3D2>Chris</FONT></DIV>
<BLOCKQUOTE=20
style=3D"PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; =
BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style=3D"FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV=20
style=3D"BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: =
black"><B>From:</B>=20
<A title=3Dbstirton@austin.rr.com =
href=3D"mailto:bstirton@austin.rr.com">Broc=20
Stirton</A> </DIV>
<DIV style=3D"FONT: 10pt arial"><B>To:</B> <A =
title=3Dmythtv-dev@snowman.net=20
href=3D"mailto:mythtv-dev@snowman.net">mythtv-dev@snowman.net</A> =
</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Sent:</B> Thursday, November 14, =
2002 6:06=20
PM</DIV>
<DIV style=3D"FONT: 10pt arial"><B>Subject:</B> RE: [mythtv] VGA to =
NTSC scan=20
converter</DIV>
<DIV><BR></DIV><BR>On Thu, 14 Nov 2002, Jeremy Oddo wrote:<BR><BR>> =
><BR>> > Does any one have any info on what refresh =
would<BR>>=20
> theoretically work best with a scan converter? My first =
instinct=20
(60Hz)<BR>> > proved to most defintely not be the best =
looking.<BR>>=20
><BR>> Seriously? I would have guessed 60Hz as well, =
seeing as how=20
NTSC<BR>> refreshes each field at 60Hz (well, 59.94Hz) I =
would have=20
guessed that<BR>> refreshing faster wouldn't make a =
difference. =20
Interesting indeed. Of<BR>> course, PAL refresh is=20
50Hz.<BR>><BR><BR>That was my reasoning (I live in Texas, so NTSC =
here),=20
but the 60Hz<BR>modelines for 800x600 and 640x480 looked pretty =
bad. =20
IIRC, it was more<BR>flickery. My unit has a flicker filter (not =
sure=20
how good), but maybe the<BR>small diff between the NTSC 59.9xx sync =
and 60Hz=20
is the problem=20
=
(?)....<BR><BR>_______________________________________________<BR>mythtv-=
dev=20
mailing list<BR><A=20
=
href=3D"mailto:mythtv-dev@snowman.net">mythtv-dev@snowman.net</A><BR><A=20
=
href=3D"http://www.snowman.net/mailman/listinfo/mythtv-dev">http://www.sn=
owman.net/mailman/listinfo/mythtv-dev</A></BLOCKQUOTE></BODY></HTML>
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