[FFmpeg-user] Meaning of ffprobe output

Ulf Zibis Ulf.Zibis at gmx.de
Thu Feb 21 12:31:41 EET 2019

Am 21.02.19 um 01:41 schrieb Carl Eugen Hoyos:
> 2019-02-04 23:29 GMT+01:00, Ulf Zibis <Ulf.Zibis at gmx.de>:
>> Now I've checked the files with mediainfo:
>> - The vob file is stated as interlaced top first. (I know, this does
>> nothing say about the content, only the flag is evaluated.)
> Doesn't FFmpeg also report this?
> (I believe it should.)
This is what I had asked several times, what the meaning of the string
"top first" on the vob input is. It's just the indication of the flag or
something else?

>> - The transcoded mp4 is stated as progressive.
> Did you specify that you want x264 to encode using
> algorithms for interlaced input material?
> Should be "-flags +idct"
Aha, this appears to be the long awaited answer to my question what you
mean by "encoded interlaced". The x264 encoder has a special
mode/optimization for interlaced material, which should be enabled
manually, as the encoder can't detect the nature of the input material
automatically. So I guess, the interlaced flag is set automatically when
"-flags +idct" is used, but never just copied from the input stream.

>> I don't know, why libx264 doesn't retain the flag, maybe it evaluates
> Again (afair, I already wrote that at some point):
> x264 neither retains nor drops "the flag", it doesn't know
> about the input content, it cannot "evaluate" its content.

Hm, as mediainfo shows, the flag "interlaced top first" was dropped when
transcoding from vob to mp4, which seems to be the same what
ffmpeg/ffprobe states by the string "top first".

>> I still must admid, that I don't really understand what is meant by
>> "encoded interlaced", is it the same than "has the interlaced flag set"?
>> I see no reason why ffmpeg "cannot know" this flag. 
> Of course it knows this flag but since the flag is completely useless
> (for encoding, it may be needed to decode correctly) it cannot be
> used to determine correct settings for encoding.
> Allow me to repeat: Except for the intro, the video you provided
> is not interlaced, it has artefacts that may or may not be easier
> to encode when using interlaced encoding.
> (Because of the given quality, this is mostly a moot discussion:
> Just use a low quantiser or keep the "originals", if you are really
> interested in the movie buy a dvd that will beat the quality of
> your recording by far.)
In the meantime I had the chance to phone with the original producer
Moritz Boerner. The film was recorded with 36 mm celluloid and he had
above 250.000 DM, not 20.000 DM to produce the film.
So I buyed the DVD now. Except that it has 3 audio tracks to choose and
the VHS head switching artefacts are missing, it unfortunately has the
equal bad quality than my DVD recorder copy, but even has a worst colour
quality than my copy. The purchased DVD is not a direct telecined copy
from the 36 mm material (disappointing), it seem to be a capture of the
in earlier times provided VHS cassette, but with a better adjusted VHS
player, so the head switching artefacts are missing.

> PS: Rethinking, it may be a good idea to add the flags for
> your x264 encoding, I believe the encoder is smart enough
> to decide when / how to use it. I suspect it won't make a
> difference for the native FFmpeg video encoders though.

Is native vs. x264 encoder something different?


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