[mythtv] Interlaced vs. Progressive

David Asher david.asher at caviumnetworks.com
Sun Feb 26 05:14:01 UTC 2006

I've been following the development of the Internal video player closely 
because I'd love to punt xine for displaying MythVideo stuff -- esp. 
with the advent of DVD menu support.

But every time I've used it on an .avi (or DVD .iso), the picture 
quality has been terrible.  I never bothered to look into why until 
today.  It turns out that it appears to be entirely attributable to the 
internal player thinking progressive video is interlaced -- and applying 
the deinterlacer to it.  If I disable the deinterlace in TV playback 
options the quality is quite good.

It appears the "culprit" is detectInterlace which simply says (for non 
720 video) if the fps is <= 45 it must be interlaced.  These videos all 
report ~23.97fps (DVD reports 29.997fps).  Of course there is the 
following comment too:

        // The scanning mode should be decoded from the stream, but if it
        // isn't, we have to guess.

So, obviously, I need to figure out why progressive/interlaced isn't 
being "decoded from the stream".

I'm happy to look into coding an improved interlace detector -- but 
don't have the slightest idea where to start.  Anybody willing to point 
me in the right direction?  Other players which do it better learn 
from?  I suppose I could resort to adding a key to toggle deinterlace 
from the player...  That's pretty icky, though.



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