[mythtv-users] Nvidia tvout picture quality

john roberts homepagez at lycos.com
Tue Sep 14 08:48:34 EDT 2004

Ah!  This is something I've been spending way too much time on recently.

I've got a 50inch DLP which up/down converts things to 1280x720p.  I've tried mythtv with/without XvMC, with/without various de-interlace methods and I agree with the previous post about the step down in content quality with XvMC.

I was using XvMC because for the life of me I couldn't get ATSC content to not stutter without it.  BUT!!!  SOMETHING VERY COOL happened last night. :)  I was able to get the new switch resolution feature within 0.16 to work!!!

And that's where its at - IMHO.  The quality is better and no more stutter for me.  XvMC has been disabled and I'm doing eveything under Xv.

This assumes your TV does as good (or better) job of de-interlacing the 1080i content (and assuming your TV converts things to 720p).

The Samsung seems to have very good support for accepting an interlaced signal and doing the de-interlacing for me.

So - after much mucking around and re-compiling with different settings/options/etc - I think I'm done.  No more XvMC for me anyway.  (Not that it was THAT bad - it's just a bit better with Xv IMHO).


----- Original Message -----
From: Doug Larrick <dougl at charter.net>
Date: Tue, 14 Sep 2004 06:45:35 -0400
To: Discussion about mythtv <mythtv-users at mythtv.org>
Subject: Re: [mythtv-users] Nvidia tvout picture quality

> David Collett wrote:
> > - no deint + no xvmc = total crap (visible interlacing artifacts), CPU=?
> > 
> > - no deint + xvmc = very smooth, no visible interlacing artifacts (xvmc
> > doesnt seem to need a deinterlaced signal?), but visual quality is not
> > great(colours not as vibrant, appears 'grainier'), CPU=20%
> > 
> > - deint + xvmc = smooth, but blocky, the deint seems to screw with xvmc
> > to the point where it looks better without it. Also, I have had frontend
> > crashes with some deint algos + xvmc. CPU=20%
> > 
> > - deint + no xvmc = excellent visual quality (varies slightly depending
> > on deint algo), but not quite as smooth as xvmc. CPU=60%
> A few notes:
> The deinterlacing filters cannot run with XvMC turned on.  The decoding 
> is done in the video card, so there's nothing to filter.  XvMC does, 
> however, pay attention to the deinterlace *setting*.  It chooses one of 
> three things:
>    - if the video is progressive scan, it send both fields
>    - if the video is interlaced and deinterlacing is turned off, it 
> sends the first field (poor-man's deinterlacing, same idea as the 
> 'onefield' deinterlacer.
>    - if the video is interlaced and deinterlacing is turned on (doesn't 
> matter which method), XvMC uses the equivalent of bob deinterlacing: it 
> displays first one field then the other, at double the framerate.
> Read a post I made yesterday for a description of what the various 
> filters do.
> I use no xvmc + bob deinterlace filter for output to my (1080i-native) 
> HDTV.  For me this is the best combo.
> -Doug
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