[FFmpeg-trac] #4814(undetermined:new): swscale default alpha blending drops alpha

[FFmpeg]

#4814: swscale default alpha blending drops alpha
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             Reporter:  michael      |                    Owner:
                 Type:  enhancement  |                   Status:  new
             Priority:  normal       |                Component:
              Version:  unspecified  |  undetermined
             Keywords:  swscale,     |               Resolution:
  alpha                              |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
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.

 I'd also like proof that there are files with garbage in the alpha
 channel, that work fine with their native software (i.e. the software that
 invented the format or is designed to work with the format, like QT for
 prores).

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Ticket URL: <https://trac.ffmpeg.org/ticket/4814#comment:4>
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