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

[Christian Ebert]

* Carl Eugen Hoyos on Monday, January 07, 2013 at 16:05:01 +0000
> 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).

Non-commercial PAL DVDs here. Either created with mjpegtools or
by shops which create actors' showreels.

> But perhaps you mean telecined?

No.

>>>> 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.

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.

I also have the reverse case: PAL movs processed with the Bitvice
denoise filter, which also offers a deinterlace option: no
deinterlacing needed. Again mediainfo confirms my visual
inspection, idet is neither here nore there when it comes to the
decision whether I should deinterlace 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.

Fine with me. For my use cases I trust my own eyes, and so far
mediainfo gave me correct results. I would not hesitate to turn
over mediainfo's judgement if it mislead me.

Furthermore mediainfo tells me about bitrate peaks for instance
in m4a files where ffprobe -show_streams at least only shows the
average bitrate.

I can't argue with the theoretical background, but at least for
my practical purposes mediainfo delivers with astonishing
reliability in some areas where ffmpeg or ffprobe did not help.

c
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