[FFmpeg-user] Source v210.mov has no interlacement info, ffv1 transcode is listed as progressive

[Kieran O Leary]

Hello Jerome!!

On Thu, Jul 28, 2016 at 5:06 PM, Jerome Martinez <jerome at mediaarea.net> wrote:
> Le 28/07/2016 à 10:38, Kieran O Leary a écrit :
>>
>> Hi,
>>
>> My  input file was generated from Avid Media Composer 8.
>> Link: https://www.dropbox.com/s/yed44wj5lq9jg8h/2fr.mov?dl=0
>>
>> If I use -c copy to remux to mov or mkv, then the lack of
>> interlacement info is maintained. When I encode with FFV1, using
>> either MKV or MOV, the file is listed as progressive in mediainfo.
>>
>> However, the issue may not be specific to FFV1 as progressive values
>> appear in mediainfo when using -c:v prores (in mov container) and
>> libx264 in mov and mkv.
>
>
> The difficulty here is to define "progressive": is it how it is coded or how
> it should be displayed?
> your input is coded progressively (one v210 frame) despite the fact (you
> affirm it) your ingest is TFF (there is no info about it in the input file).
> I guess that FFmpeg considers by default that v210 is always to be displayed
> progressive and sets the FFV1 encoder to progressive (value 3) instead of
> "unknown" (value 0) in the FFV1 bitstream.
>

Thanks for the explanation. It would seem that the file is encoded
progressively but is to be displayed top field first. I think of all
the outcomes  - a. specifying the correct field order, b. leaving
field order undeclared as in the source, c. output is labelled
progressive - option c is my least favoured option.

> You can force FFmpeg to configure the encoder with interlacement.
> ffmpeg -i 2fr.mov -vf "interlace=lowpass=0:scan=tff"  -c:v ffv1 -level 3
> out.mkv
> https://ffmpeg.org/ffmpeg-all.html#interlace
>
> and your FFV1 stream is coded as interlaced (with an improvement about file
> size)
> (note: the result is interlaced but looks like there is only 1 frame instead
> of 2, please double-check the command line; I am not a FFmpeg expert so a
> better command line would be appreciated)
>
> But please use it only if you are sure about your input because other people
> will rely on this information.
>

Thanks for the tip. I tried your command and it resulted in 12.5fps
(which is probably intentional?) , and the pix_fmt defaulted to
yuv422p, so I'll stay away from this route.  Using field_order to
specify the field order in the source and then transcoding to ffv1
seems to work ok and produces matching framemd5s. Quicktime and VLC do
not seem to play the files back any differently, whether the field
order is undeclared or TFF though.

Best,

Kieran.