[FFmpeg-trac] #8509(avcodec:new): Converting 8 bit ARGB to Prores 4444 using prores_ks produces alpha channel that is not 100% opaque

[FFmpeg]

#8509: Converting 8 bit ARGB to Prores 4444 using prores_ks produces alpha channel
that is not 100% opaque
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             Reporter:  bford       |                    Owner:
                 Type:  defect      |                   Status:  new
             Priority:  normal      |                Component:  avcodec
              Version:  git-master  |               Resolution:
             Keywords:  prores      |               Blocked By:
             Blocking:              |  Reproduced by developer:  0
Analyzed by developer:  0           |
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Comment (by bford):

 Yes, that resolves the issue!

 I think I can see what you've done there..  255 << 6 = 16320 (not 16384),
 so you have to account for the difference by adding (255 >> 2) = 63.

 Thank you very much for investigating this for me!

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Ticket URL: <https://trac.ffmpeg.org/ticket/8509#comment:6>
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