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

[Carl Eugen Hoyos]

Christian Ebert <blacktrash <at> gmx.net> writes:

> * James Darnley on Wednesday, December 19, 2012 at 14:50:06 +0100
> > On 2012-12-19 13:12, Christian Ebert wrote:
> >> Hm, a vob file for instance is in all probability interlaced, and

I own a few dvd's, they are all progressive (they are all movies 
or television series that usually cannot be interlaced), only 
very few samples in our database are interlaced DVD, typically 
music or live television recordings (or both).

But perhaps you mean telecined?

> >> at least it "looks" like in this case for once mediainfo gives
> >> more meaningful info:
> >> 
> >> $ mediainfo --Inform='Video;%ScanType%' test.vob
> >> Interlaced
> >> $ mediainfo --Inform='Video;%ScanOrder%' test.vob
> >> TFF
> > 
> > This tells you absolutely nothing about the *content* and is of no more
> > use than ffmpeg's flags about the manner in which a video was encoded.
> 
> Fair enough. It's very useful though when I want to know whether
> I need to apply a deinterlace filter or not. The idet filter does
> not help then.

I wonder what you mean here.
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.
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.

So I really don't see in which situation "the idet filter 
does not help" - actually it is exactly the other way round.

Carl Eugen