[mythtv-users] New deinterlacer for perfect image quality when using an interlaced display, mode that matches the source

[Paul Gardiner]

Tom Dexter wrote:
> On Thu, Mar 26, 2009 at 8:26 AM, Paul Gardiner <lists at glidos.net> wrote:
>> I've just created a patch that provides a deinterlacer for perfect image
>> quality and motion smoothness when using an interlaced display mode that
>> exactly matches the video source. See Ticket #6391. The deinterlacer comes
>> up in the menus as "Interlaced x2". It is also known as field order.
>>
> 
> Very very cool stuff Paul.  I was reading about this on your thread on
> the dev list.
> 
> I've been running 0.21-fixes version 18314 under Gentoo patched with
> that 2903 patch to allow Bob x2.  I watch all U.S. OTA DTV on a rear
> projection CRT (Hitachi 51F500), so my issues have been mainly with
> 1080i content.  In my case the 2903 patch and Bob have worked well,
> though never quite as good as with no deinterlacing (when it happened
> to be in sync, which certainly wasn't often enough to put up with).
> 
> ...
 >
> In any case I got it to work and I'm only having one issue (not the
> fault of your code...more on that below).  I have to say that this is
> the first time I've seen my myth system play 1080i content and have it
> look just as good as my Samsung HD receiver.  From my testing so far,
> this appears to be exactly what I've been hoping for since building
> the system two years ago, and may be just as good as actually having
> nVidia fix their 1080i ouput (which may never happen).

Great news. I wondered whether it could work with 1080i. Sounds like
you've been in a similar position to me, having other equipment that
could give slightly better image quality, and never quite being able
to give up on making mythtv do as well.

The bit about nVidia confuses me a bit. I've obviously not understood
what the problem they have with 1080i because I was expecting it to
prevent use of the fieldorder patch; I thought it caused line doubling
when using XV rendering. What is that actual problem? Is it just the
problem of getting two vsyncs per frame?

> The issue I'm running into is due to the fact that two of my 1080i
> stations...NBC and CBS...have the unexplainable practice of mixing
> progressive and interlaced frames.  This causes the constant
> re-enabling of interlacing every 1/2 second or so:
> 
> 2009-03-26 14:08:04.288 Using deinterlace method fieldorderdoubleprocessdeint
> 2009-03-26 14:08:07.491 NVP: progressive frame seen after 91 interlaced  frames
> 2009-03-26 14:08:07.558 Enabled deinterlacing
> 2009-03-26 14:08:07.808 NVP: interlaced frame seen after 9 progressive frames
> 2009-03-26 14:08:07.808 Enabled deinterlacing
> 2009-03-26 14:08:08.094 NVP: progressive frame seen after 10 interlaced  frames
> 2009-03-26 14:08:08.163 Enabled deinterlacing
> 2009-03-26 14:08:09.274 NVP: interlaced frame seen after 29 progressive frames
> 2009-03-26 14:08:09.274 Enabled deinterlacing
> 2009-03-26 14:08:09.458 NVP: progressive frame seen after 7 interlaced  frames
> 2009-03-26 14:08:09.524 Enabled deinterlacing
> 2009-03-26 14:08:10.791 NVP: interlaced frame seen after 33 progressive frames
> 2009-03-26 14:08:10.791 Enabled deinterlacing
> 2009-03-26 14:08:11.091 NVP: progressive frame seen after 10 interlaced  frames
> 2009-03-26 14:08:11.158 Enabled deinterlacing
> 
> ...etc...etc.  This issue (especially with NBC) has come up on the
> list before.  It doesn't seem to cause visible issues with Bob x2 for
> some reason.
> 
> However, as long as this occurs using fieldorderdoubleprocessdeint I
> run into various problems including occasional tearing.  However, if
> immediately after starting playback, I pause and then go into the
> playback menu and change the video scan from "Detect" to "Interlaced
> (Normal)" your deinterlacer seems to work flawlessly...at least from
> what I've seen so far.  Forcing that setting has actually been the
> recommended work-around when this issue has been raised here before.
> 
> Definitely cool beyond belief though.  I'm going to look into seeing
> if I can find a way to patch playback so that, as soon as
> deinterlacing gets enabled after seeing any progressive frames (which
> doesn't seem to ever happen on any of my actual 720p channels), it
> simply leaves deinterlacing on.  In my case that would take care of
> it.

That sounds like an ideal patch. Hope you can get that working. Will
also be handy for me when I eventually go HD here.

The other thing I wonder about is whether we can get 2903 committed.
Perhaps it could be made a configuration option with default being off.
I haven't yet figured out how one adds new config options though.

Cheers,
	Paul.