[FFmpeg-trac] #4746(swscale:closed): prores alpha blending results in opaque rectangle

[FFmpeg]

#4746: prores alpha blending results in opaque rectangle
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             Reporter:               |                    Owner:
  projectsymphony                    |                   Status:  closed
                 Type:  defect       |                Component:  swscale
             Priority:  normal       |               Resolution:  fixed
              Version:  git-master   |               Blocked By:
             Keywords:  prores       |  Reproduced by developer:  1
  alpha                              |
             Blocking:               |
Analyzed by developer:  0            |
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Comment (by gjdfgh):

 You forgot PNG, that essentially requires the same behavior as prores.

 laraShadow_dl.flv unfortunately just shows black when blending against
 black, but have you considered that the result is not better AT ALL when
 just discarding the alpha channel?

 From what I see, blending against black (or maybe blending against a
 checkerboard) is still the sanest default behavior.

 And the ONLY reason our bug tracker terrorist rejects this new default
 behavior is because it's "slower". A typical example of "fast and wrong is
 better than correct and not-turbo-fast". Which is incidentally also the
 reason why ffmpeg fucks up so often (preferring speed over correctness).

 >@gjdfgh (I guess that is @kierank)

 No, wm4.

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Ticket URL: <https://trac.ffmpeg.org/ticket/4746#comment:43>
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