Field order inversion using ffmpeg

[cjdavis83]

Hi,

I was wondering what phase command I should use for inverting the field order of an NTSC video source in ffmpeg captured wrongly as TFF using hardware
It is pure analog NTSC video but TFF was used by default during the capture process.

phase = b or = phase t

??

I was using fieldorder=bff but I understand that some blurring of chroma may be induced.

[poisondeathray]

separate the fields, discard the 1st field, weave it back together

-vf setfield=tff,separatefields,trim=start_frame=1,weave,setfield=bff

[cjdavis83]

separate the fields, discard the 1st field, weave it back together

-vf setfield=tff,separatefields,trim=start_frame=1,weave,setfield=bff

This will give me pure interlaced video with bottom field first?

[poisondeathray]

separate the fields, discard the 1st field, weave it back together

-vf setfield=tff,separatefields,trim=start_frame=1,weave,setfield=bff

This will give me pure interlaced video with bottom field first?

If you started with pure interlaced content TFF, and your timestamps are ok , it should work. But sometimes ffmpeg produces unreliable results if the input timestamps have problems

If you have problems, then you can use avisynth with a frame accurate source filter - and it will work for certain. Avisynth is more consistent for this type of work than ffmpeg

#Input
AssumeTFF()
SeparateFields()
Trim(1,0)
Weave()

If you still have problems, post a stream copied video sample of the source

[cjdavis83]

separate the fields, discard the 1st field, weave it back together

-vf setfield=tff,separatefields,trim=start_frame=1,weave,setfield=bff

This will give me pure interlaced video with bottom field first?

If you started with pure interlaced content TFF, and your timestamps are ok , it should work. But sometimes ffmpeg produces unreliable results if the input timestamps have problems

If you have problems, then you can use avisynth with a frame accurate source filter - and it will work for certain. Avisynth is more consistent for this type of work than ffmpeg

#Input
AssumeTFF()
SeparateFields()
Trim(1,0)
Weave()

If you still have problems, post a stream copied video sample of the source

Here is the TFF sample that was captured wrongly;

https://drive.google.com/file/d/1jBa6BUfnov-4cxq-D2gmlNX6GqgcHo1K/view?usp=drivesdk

[poisondeathray]

The ffmpeg command above does not work properly; You might have to use filter_complex and separatefields split the outputs into even and odd streams, trim 1st even, and interleave them back. It's tricky because it messes up the PTS, so you need a PTS expression. I'll play with it and see if I can get it to work

avisynth works, as expected

LSmashVideoSource("longsample_480i_tff.mov")
AssumeTFF()
SeparateFields()
Trim(1,0)
Weave()
AssumeBFF()

(There are some experimental ffmpeg builds that accept avs properties, so if it was flagged BFF, that would be read as BFF instead of having to set it in ffmpeg)

But to encode it with any ffmpeg build

ffmpeg -i bff.avs -i longsample_480i_tff.mov -map 0:0 -map 1:1 -flags +ildct+ilme -top 0 -vf setfield=bff -c:v prores -profile:v 3 -c:a copy avs_bff.mov -y

So that results in content BFF, and en coded and flagged BFF

But a question is why do you need BFF ? TFF is perfectly acceptable for SD content . You incur generation loss if you encode with lossy format like prores

[poisondeathray]

Actually I forgot about these:

-vf fieldorder
-vf phase

https://forum.videohelp.com/threads/365238-how-to-invert-field-order-with-ffmpeg

This works ok

ffmpeg -i longsample_480i_tff.mov -vf "fieldorder=bff" -c:v prores -profile:v 3 -flags +ildct+ilme -top 0 -c:a copy output.mov

-vf "phase=mode=t" worked mostly ok too, but there was a glitch in the 2nd field