[FFmpeg-trac] #6590(undetermined:new): weave filter produces video with incorrect field order

[FFmpeg]

#6590: weave filter produces video with incorrect field order
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             Reporter:  alexz         |                     Type:  defect
               Status:  new           |                 Priority:  normal
            Component:  undetermined  |                  Version:  3.2.4
             Keywords:                |               Blocked By:
             Blocking:                |  Reproduced by developer:  0
Analyzed by developer:  0             |
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 Summary of the bug:

 weave filter produces interlaced video with an incorrect field order

 How to reproduce:

 1. Create sample video (horizontally moving box) with a double frame rate
 (50)
 {{{
 ffmpeg -f lavfi -i "color=color=blue:size=352x288:rate=50:duration=3" \
     -vf "color=white at 1:size=50x50:rate=50:duration=3 [box]; [in][box]
 overlay=n*hsub:10" \
     -codec:v ffv1 -level 3 output-50p.mkv
 }}}

 2. Make an interlaced video with the first field top using weave filter
 {{{
 ffmpeg -i output-50p.mkv -aspect 4/3 \
     -vf "weave=first_field=t" \
     -codec:v ffv1 -level 3 output-25i.mkv
 }}}

 Despite mediainfo correctly identifies the resulting video (output-
 25i.mkv) as interlaced with the top field first, video playes "jerky".
 This is points to an incorrect field order.

 Also the incorrect field order is visible in the frame's pictures,
 extracted with
 {{{
 ffmpeg -i output-25i.mkv %03d.png
 }}}

 Attached patch fixes the issue.

--
Ticket URL: <https://trac.ffmpeg.org/ticket/6590>
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