[mythtv] Internal DVD player incorrectly detects video scan (interlacing)

Matt Doran matt.doran at papercut.biz
Wed May 30 07:23:34 UTC 2007

Hi there,

Below is a discussion from the users list that didn't produce any 
answers.  I'd be interested on working on a patch to try to fix the 
issue, but I need some guidance/ideas on where to start.

In summary, the issue is that the video scan detection for some DVDs 
(but not all DVD) seems to incorrectly choose progressive scan, which 
results in an awful jerky looking video (almost like it's skipping every 
second frame).  If I override the video scan setting it to "interlaced" 
to output is perfect.  The detailed explanation and some -v playback 
logs are described below.

 From the logs it seems that it starts off in interlaced mode 
correctly.  But as some point it thinks it sees a progressive frame so 
switches off the interlacing.

I'm using a very recent trunk build.  I have bob deinterlacing and 
OpenGL vsync enabled, and an Nvidia 6150 graphics card.

Any ideas on what could be causing this, or where I should start to fix 
this would be appreciated.


Matt Doran wrote:
> Matt Doran wrote:
>> stanley kamithi wrote:
>>> add  inverse telecine filter (ivtc) to your custom filter list.
>>> sounds like some of your  dvds has telecined output.
>> Hi Stanley,
>> I don't know anything about telecined output.  If I add this to the 
>> custom filter, will this impact TV at all?   My TV output is now very 
>> good, and would not want to affect that if possible.
>> Can I apply the filter to DVD only?
>> I'll give it a try tonight.
> Hi Stanley,
> I don't think this is a telecine issue.  I'm in Australia, so my DVDs 
> are mostly PAL.   However, one DVD I can reproduce the problem on is a 
> "West Wing" import ... so I'm not sure of the standard it's using.  The 
> other was a DVD I rented and have returned ... but would have been PAL.
> I've added "ivtc" to my custom filters, but it hasn't had any effect.  I 
> haven't seen the line "turning on inverse telecine filter" on stderr 
> (which I can see in the code) so I don't think it's switched on.  Any 
> way that I can confirm?
> I've attached the output of 2 -v playback for two different examples.  
> They both show interlacing is used in the startup sequence, the first 
> one switches to progressive when I press play, the second switches to 
> progressive when I go to the "Episodes" submenu even though it has no 
> video content and nothing is playing.
> Time sequence for frontend-play1.log
>     * 20:1 7:40 - start dvd, playing startup sequence.  Startup sequence
>       is interlaced, and plays fine.
>     * 20:18:21 - pressed play once startup completed.  Changes to
>       progressive, and looks awful
>     * 20:18:50 - Manually change video sync to "Interlaced".  Looks
>       fine  again
> Time sequence for frontend-play2.log
>     * 20:23:35 - start dvd, playing startup sequence.  Startup sequence
>       is interlaced, and plays fine.
>     * 20:24:16 - selected the "Episode" menu.  Changes to progressive,
>       even though there is no video content.
>     * 20:18:21 - select an episode to play.  Still in progressive mode,
>       looks awful
>     * 20:18:50 - Manually change video sync to "Interlaced".  Looks fine
>       again
> What do you think?  It definitely seems to be detecting the progressive 
> frames incorrectly.   I'm happy to help in anyway and provide any info 
> that could be of assistance.
> (I'm running trunk r13509, and can easily test patches and/or recompile 
> if necessary.)
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