[mythtv-users] Stupid question - deinterlacing

Paul Gardiner lists at glidos.net
Sun Feb 22 20:56:41 UTC 2009


Goga wrote:
> yes. you are right -  nvidia cards (and ati too) can't work properly with interlaced video 
> there's project about that issue, but only for ATI Radeon cards
> http://lowbyte.de/vga-sync-fields/vga-sync-fields-0.0.10/README
> ========================================================================
> This is a patch collection with some additional tools allowing you to 
> synchronize VGA video timing to an external signal source. This way 
> you may overcome common problems on today's PC VGA compatible hardware
> when being used as frontend for live TV.

I believe there are three different problems here.

1) Getting the card to output a correctly interlaced signal
that a TV can lock up to.

2) Avoiding any processing (such as scaling) so the content's
interlaces can be mapped to the interlaced signal. I think this
is where the nVidia driver falls down. It seems impossible
to use XV without destroying interlaced content.

3) Avoiding the fields being synced out by one.

ATI cards using the xf86-video-ati driver have worked fine in
this mode going back several years, in as much as they don't
have problems with 1 and 2. Recently xf86-video-ati broke
interlaced output, but that was temporary. It's back working
now. (I've been experimenting with it).
http://bugs.freedesktop.org/show_bug.cgi?id=19323

As far as I can see, what is new about this vga-sync-fields
project is that it tries to deal with Problem 3. I think the
approach may be overkill. All that is needed is to use the
deinterlacer known as "Interlaced". It's the one that turns
interlaced 25fps frames of the form

   12 34 56 78

into 50fps frames of the form

   12 32 34 54 56 76 78

Using this deinterlaced doesn't avoid synchronisation happening,
but makes the picture look fine at any synchronisation.
The problem with this deinterlacer is that it's available in
MythTv only when using OpenGL. I've been meaning to create a software
version, but the temporary breaking of xf86-video-ati, and also
my TV having to be sent off for repair has delayed my setting up
of hardware.

Cheers,
	Paul.



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