[FFmpeg-user] Capture from USB Dazzle: Interlaced or not interlaced. FFV1 level3 vs h264

Andy Furniss adf.lists at gmail.com
Sat Oct 31 14:21:40 CET 2015

MrNice wrote:

> Carl Eugen said on Dec 19, 2012: "To the best of my knowledge, only
> visual inspection tells you, ..."

Yes or idet as you have found which also gives the field dominance info
you need. Without idet, to find tff/bff  you would need to deinterlace
with say yadif=1 while setting dominance with its options or -vf
setfield= and see what looked correct. Motion will be jittery with the
wrong setting especially obvious if you frame step with a player.

> so, what I did and all the 4 files, (FFV1/h264, with/without -flags
> +ilme+ildct) are definitely interlaced without any doubt.

Ideally the v4l would pass on info about field dominance and ffmpeg
would use it.

I don't know whether this info is available or not.

Maybe the output from -loglevel debug when using v4l will show
something/nothing about field dominance so we can judge whether ffmpeg
has an issue or v4l.

> However tags are not consistent: FFV1 with -flags:
> interlaced_frame=0, top_field_first=0 FFV1 without -flags:
> interlaced_frame=0, top_field_first=0 h264 with -flags:
> interlaced_frame=1, top_field_first=0 h264 without -flags:
> interlaced_frame=0, top_field_first=0

For x264 it seems that flags is just passing info (tff) to the lib - as
I already said there are other ways to do this, which also let you
choose tff/bff.

It seems flags/x264-opts are not alone enough you need also to use eg.
-vf setfield=tff

As it seems flags does nothing at all for ffv1 -level 3 you just need

> Questions: - How to get interlaced_frame=1 with FFV1? - Could you
> confirm top_field_first=0 means bff and really what is in the file?

It does mean bff, but from your further tests it's clearly wrong/just
not been set by anything.

> - BTW I have read bff is the usual setting for DV, do you agree I
> should keep it like that?

Other things can be bff, in this case you now know it's not OK to keep it.

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