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

MrNice wxcvbn2006 at iol.ie
Fri Oct 30 18:09:08 CET 2015

On 29/10/15 20:09, Andy Furniss wrote:
> Carl Eugen Hoyos wrote:
>> MrNice <wxcvbn2006 <at> iol.ie> writes:
>>> When I capture some video with the CL ./ffmpeg -debug 1 -f v4l2 -ts
>>> mono2abs -channel 1 -video_size 720x576 -pix_fmt yuyv422
>>> -thread_queue_size 512 -i /dev/video0 -c:v ffv1 -level 3 -g 1
>>> -aspect 4:3 -pix_fmt yuv422p /Store3/Test/t_`date
>>> +%Y%m%d_%H%M`.mkv -aspect 4:3 -f sdl "Dazzle output"
>>> from a S-VHS tape and Dazzle DVC100, I was thinking to get an
>>> interlaced video file.
>> Why? I mean: How is FFmpeg (or the FFV1 encoder) supposed to know
>> that your v4l input is interlaced?
> Hopefully the device/v4l would pass on this information.
>> (And why shouldn't your S-VHS recording be low-resolution
>> progressive?) Maybe I miss something but in this case please
>> explain.
> I thought s-vhs was like vhs = one field per stripe on the tape.
> Maybe if what was recorded was progressive you wouldn't care assuming
> v4l outputs weaved frames - but a lot of tape contains interlaced so you
> would need the field dominance info for that.
> Random thought - as it's analogue field input, I wonder if it's possible
> that even with a progressive recorded as interlaced you could end up
> with weaved frames that don't "line up".
> _______________________________________________

Carl Eugen said on Dec 19, 2012: "To the best of my knowledge, only
visual inspection tells you, ..."
so, what I did and all the 4 files, (FFV1/h264, with/without -flags
+ilme+ildct) are definitely interlaced without any doubt.

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

- How to get interlaced_frame=1 with FFV1?
- Could you confirm top_field_first=0 means bff and really what is in
the file?
- BTW I have read bff is the usual setting for DV, do you agree I should
keep it like that?

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