[FFmpeg-user] When to determine frames are progressive or interlaced ?

Christian Ebert blacktrash at gmx.net
Mon Jan 14 09:26:34 CET 2013


* Carl Eugen Hoyos on Monday, January 07, 2013 at 22:25:50 +0000
> Christian Ebert <blacktrash <at> gmx.net> writes:
>>> I suspect (and it is what James writes above) that mediainfo 
>>> only tells you if the video was encoded using an encoder 
>>> setting "interlaced" or not. It does not tell anything about 
>>> the actual content.

Right. mediainfo only inspects metadata, I guess.

>>> If you use a deinterlacer on progressive content (no matter 
>>> if it was encoded as "interlaced" or not), you permanently 
>>> damage the frames. Otoh, you can encode interlaced material 
>>> as "progressive" (or use an encoder that does not support 
>>> "interlaced") and only visual inspection or a filter like 
>>> idet will tell you if you should use a deinterlacer or not.
>> The result by mediainfo coincides with my visual inspection - I
>> can see it right away when I play the files in mplayer without
>> yadif: blatantly obvious vertical lines in the picture - with
>> yadif the picture is fine. Encoding without deinterlacing looks
>> just awful.
> So I stand corrected, maybe the reason is that most of my 
> experience is with Transport Stream where I know as a 
> fact that they typically signal "interlaced" even for 
> progressive material, maybe this simply does not 
> happen for DVD's.

Sorry for getting back late, I found time (in the literal sense)
to test more extensively, and it looks like basically I did not
let run idet long enough to obtain good results. I also now found
a sample from a DVD where deinterlacing is not needed in spite of
mediainfo talking about scan type interlaced. While I could not
detect any visual damage when running the unneeded deinterlace
filter in a test encoding, I now ruefully concur that the idet
filter is more precise - otoh I'm quite happy that I can ditch
mediainfo for some of my scripts.

There are still some cases where mediainfo output comes in handy,
but on the whole it's probably less precise than ffprobe or

Thanks for persisting and convincing me.

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