[mythtv-users] Any hope for 1080i content at 1080i with nVidia?

Steve Smith st3v3.sm1th at gmail.com
Tue Jul 31 08:50:41 UTC 2007


On 30/07/07, Tom Dexter <digitalaudiorock at hotmail.com> wrote:
>
> >From: "Steve Smith" Date: Mon, 30 Jul 2007 12:32:00 +0100
> >
> >
> >Never mind 1080i what about 576i (ignoring TVOUT chips which seem
> basically
> >broken in this respect) ?!?!
> >
> >It seems the simple problem is that FRAME sync (rather than FIELD sync)
> >just
> >isn't working
> >somewhere along the line...
> >
> >We shouldn't need to deinterlace if we have an interlaced display
> (capable
> >of the relevant resolution) available, full stop, period, end of story.
> >
> >The fact that we do means that the syncing system is not working
> >somewhere along the line, maybe it's the card, maybe the nvidia driver,
> >maybe Myth ... does anyone know?
> >
> >Regarding bob deinterlace and "too small a refresh rate". There was a
> patch
> >posted on the list a few weeks ago by a guy called Viktor. Works well.
> >
> >Cheers
> >
> >Steve
>
> The whole issue with getting bob deinterlacing working by adjusting the
> refresh rate got me wondering...I couldn't remember why I wasn't using it
> with my original 1080i mode.  Then I remembered that, for one thing, it
> always gave me that error, and for another, I read in a number of places
> that you simply shouldn't use bob with an interlaced display.
>
> Out of curiosity, I tried that patch of Viktor's you mentioned (which is
> here for anyone interested):
>
> http://svn.mythtv.org/trac/ticket/2903
>
> I'm in the U.S. by the way...from your posts and his I see you're dealing
> with PAL frame rates.  I'm running Gentoo and didn't feel like making a
> custom ebuild just yet, so I simply installed manually using the Gentoo
> ebuild command editing in that code change between the unpack and compile
> steps.  The patch seemed to work just fine.  Instead of disallowing bob
> because the refresh rate was being reported at 33333, the refresh rate was
> reported as 16666, and bob worked just fine, and does look noticeable
> better
> than kerneldint.
>
> While I'm sure there are good reasons the devs didn't want to incorporate
> the patch, one comment they made on Viktor's bug report confuses me:
>
> "You also don't want to use bob-deint with an interlaced display, use
> kernel
> or linear blend when there is a resolution missmatch and no deinterlacing
> when the source and destination line count matches.
>
> See mythtv-vid branch for configuring such a setup."
>
> What do they mean by that last statement?  Isn't deinterlacing always
> disabled automatically when you view non-interlaced content?  I'm running
> 0.20.1 (svn 13344).  Whenever I watch livetv or recording from stations
> such
> as Fox or ABC, who broadcast in 720p, my logs (assuming I'm using -v
> playback) show something like:
>
> 2007-07-30 14:25:58.936 Disabled deinterlacing
>
> What are they talking about there?  I don't understand that reference to
> the
> mythtv-vid branch.
>
> Tom
>
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>
Tom,

After some hard thinking last night I realised a bit of what the developers
were getting at:

  (1) If what you are trying to play is the same resolution as your TV
***line for line** then you should be able to
       get away with no de-interlace...... that is if FRAME sync actually
worked. Which it doesn't appear to.

  (2) If however you are doing some scaling then what you are outputing
isn't line for line the same as the signal so some form of de-interlacing is
needed. When does this happen?
      One case is when you output a 16:9 format mpeg on a 4:3 TV. The mpeg
has 576 (for PAL) lines, but to get the right aspect ratio,
      this is scaled to 0.75*576=432 lines. Now our fields don't match up so
we need to modify the picture with some form of deinterlacing.

   (3) Viktor's patch, although it works, is a bit of a sledgehammer. Really
it should modify the bob code to double the refresh rate *that bob sees*
only if bob has been requested and interlace is being used. However, it
works in my case so I'm happy thanks Viktor! :-)


So in conclusion using Viktor's patch with bob deinterlace seems to work
best for me.

Cheers

Steve
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