[FFmpeg-user] Meaning of ffprobe output

[Carl Eugen Hoyos]

2019-01-29 2:16 GMT+01:00, Ulf Zibis <Ulf.Zibis at gmx.de>:
> Hi Carl Eugen,
>
> Am 19.01.19 um 14:02 schrieb Carl Eugen Hoyos:
>>> $ ffmpeg -i CYD_copy.vob -vf idet -f null -
>>> ffmpeg version 4.1-static https://johnvansickle.com/ffmpeg/  Copyright
>> Not supported here!
>>
>>> (c) 2000-2018 the FFmpeg developers
>>>   built with gcc 6.3.0 (Debian 6.3.0-18+deb9u1) 20170516
>> Not ok!
> This recommendation comes from here:
> https://trac.ffmpeg.org/ticket/7623#comment:5

(So apparently the next sentence is wrong and Lou
does offer release support - but unfortunately only
to you because he closed ticket #7697 this week
explaining there is no release support...)

> So I used the release version 4.1 from here:
> https://johnvansickle.com/ffmpeg/
> in the assumption, that it is more stable as the git build.

The release version contains more known bugs (and there
are indications that it contains more unknown bugs) and
less features than current git head and there is no release
support on this mailing list.

>>> [Parsed_idet_0 @ 0x6e71900] Repeated Fields: Neither:114683 Top:     1
>>> Bottom:     0

I believe this rules out telecined content.

>>> [Parsed_idet_0 @ 0x6e71900] Single frame detection: TFF: 18738 BFF:
>>> 12770 Progressive: 42496 Undetermined: 40680
>>> [Parsed_idet_0 @ 0x6e71900] Multi frame detection: TFF: 36759 BFF: 19705
>>> Progressive: 58193 Undetermined:    27
>> This is not conclusive, possibly mixed progressive - interlaced or
>> interlaced with many scenes without movement.
>> Visual inspection should clarify.
> Does that mean, that my vob stream is partly interlaced and partly
> progressive?
> I guess, TFF means top first frame and BFF bottom first frame, right?
>
> This is weird, as the stream comes from a DVD which was recorded from a
> VHS cassette with a hardware DVD recorder.

This basically explains it: Such material is always low-quality, I
wonder if de-interlacing is possible at all (I don't immediately see
how from a theoretical pov, feel free to prove me wrong).

> Also I do not understand, that after the transcoding to mp4 the numbers
> are different. I interpret this, that the transcoding process does some
> deinterlacing, but you say, the encoder does not. The vob with 114684
> frames at 25 fps results in 76:27.36 length, but the resulting mp4 with
> 114502 frames is 76:20.08.

(Please understand that while I completely understand that you
have different questions, it is not always easy to remember
what issues were already discussed: I am sure you can calculate
the number of frames from the duration, the vob file is likely vfr,
FFmpeg only support writing cfr to mov, the last status line
has more information.)

> How can I understand all this?

(Independently from your actual converted material that
I suspect cannot be improved anyway because of its
origin: )
Again, visual inspection is necessary if the output of idet is
inconclusive, I tested idet with a random interlaced and a
(created) telecined stream and the output looked
absolutely conclusive. Mixed interlaced, progressive and
telecined video is absolutely possible, depending on the
actual content.
It could also be that your interlaced input was already
encoded, I suspect this can break the detection.

Carl Eugen