[FFmpeg-trac] #9680(undetermined:new): scale2ref is one frame behind

[FFmpeg]

#9680: scale2ref is one frame behind
-------------------------------------+-------------------------------------
             Reporter:  Jozef        |                     Type:  defect
  Chutka                             |
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:
  undetermined                       |  unspecified
             Keywords:  scale2ref    |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug:
 When using scale2ref filter with dynamic ref size, the resized element
 does not match the ref exactly (lags 1 frame?)

 In the following example [w]hite rect grows 1px every frame and [r]ed
 tries to match. However when rendered on top of each other, the red one is
 1px smaller leaving 1px white border around.

 {{{
 ffmpeg -filter_complex
 "color=color=#000000:rate=20:size=400x400[b];color=color=#ffffff:rate=20:size=100x100,scale=width=iw+n:height=ih+n:eval=frame[w];color=color=#ff0000:rate=20[r];[r][w]scale2ref=eval=frame[r][w];[w][r]overlay[w];[b][w]overlay"
 -t 4 -y gif.mp4
 }}}

 ffmpeg version 2022-02-24-git-8ef03c2ff1-full_build-www.gyan.dev
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/9680>
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