[FFmpeg-trac] #3846(avcodec:new): The output video show a wrong alpha

[FFmpeg]

#3846: The output video show a wrong alpha
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             Reporter:  Noir89         |                    Owner:
                 Type:  defect         |                   Status:  new
             Priority:  normal         |                Component:  avcodec
              Version:  git-master     |               Resolution:
             Keywords:  ProRes, alpha  |               Blocked By:
             Blocking:                 |  Reproduced by developer:  0
Analyzed by developer:  0              |
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Comment (by kurosu):

 I'm not getting what the issue really is then. The prores file generated
 by "libavcodec 56. 0.101" has an alpha channel that looks proper to me. In
 particular, not, as you describe, "whose overall value is 255".

 When decoding back the prores file into whatever image format understood
 by eg gimp and supporting alpha, the alpha channel is identical to your
 "zzblock001.tif". You seem to already confirm this.

 So, what's missing? Are you for instance reporting that a software that
 handles prores with alpha displays the prores files produced by ffmpeg
 incorrectly?

 Obviously the alpha content is in those files, as ffmpeg knows how to
 retrieve it. But maybe it is incorrectly flagged for this software?

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Ticket URL: <https://trac.ffmpeg.org/ticket/3846#comment:6>
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