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

[Matt Doran]

Hi there,

I'm running trunk, and recently enabled bob de-interlacing which has 
greatly improved the smoothness of my TV playback.

But since I've done that I've noticed some problems with DVD playback.  
Not all DVDs, but it's reproducible with some.

The DVD plays OK, fills the screen, audio sync is OK... but it looks 
like every second frame is being skipped.   I eventually twigged that it 
might be related to interlacing.  In the myth DVD menu I went to the 
"Video Sync" menu, and it was set to "Detect (P)".   When I changed this 
to "Interlaced (Normal)", everything started working correctly.... 
smooth playback again.

So it appears that the Internal DVD player is incorrectly detecting the 
interlacing. 

I've enabled -v playback debugging.  But don't really know what to look 
for.  When I'm in the DVD root menu I see this:

    2007-05-27 21:09:54.874 NVP: progressive frame seen after 640
    interlaced  frames
    2007-05-27 21:09:54.875 Set video sync frame interval to 40000
    2007-05-27 21:09:54.875 Disabled deinterlacing

And then when I start playing I get this:

    2007-05-27 21:11:12.564 NVP: 800 progressive frames seen.
    'video_output' mean = '39990.92', std. dev. = '18188.45', fps = '25.01'
    2007-05-27 21:11:15.044 AFD: HandleGopStart: Key frame distance
    changed from 12 to 10.
    2007-05-27 21:11:15.924 AFD: HandleGopStart: Key frame distance
    changed from 10 to 12.
    2007-05-27 21:11:17.284 AFD: HandleGopStart: Key frame distance
    changed from 12 to 10.
    2007-05-27 21:11:17.764 AFD: HandleGopStart: Key frame distance
    changed from 10 to 12.
    'video_output' mean = '39991.59', std. dev. = '18233.39', fps = '25.01'
    2007-05-27 21:11:21.065 AFD: HandleGopStart: Key frame distance
    changed from 12 to 11.
    2007-05-27 21:11:21.545 AFD: HandleGopStart: Key frame distance
    changed from 11 to 12.
    'video_output' mean = '39991.44', std. dev. = '19141.14', fps = '25.01'
    'video_output' mean = '39991.95', std. dev. = '18234.52', fps = '25.01'
    2007-05-27 21:11:28.562 NVP: 1200 progressive frames seen.

At this point the video output is jerky.  When I select "Interlaced" I 
see this:

    2007-05-27 21:12:00.559 NVP: 2000 progressive frames seen.
    'video_output' mean = '39613.12', std. dev. = '17924.39', fps = '25.24'
    'video_output' mean = '40370.55', std. dev. = '17952.85', fps = '24.77'
    'video_output' mean = '39992.42', std. dev. = '18307.07', fps = '25.00'
    2007-05-27 21:12:12.508 Set video sync frame interval to 40000
    2007-05-27 21:12:12.508 Enabled deinterlacing

Then everything looks good again.

What can I do to diagnose/fix the problem? 

I'm starting to submit a few patches so I'm starting to get familiar 
with the code .... so might be able to investigate ... but it could be 
over my head. :)

Thanks,
Matt