[FFmpeg-trac] #6718(undetermined:new): Option to remove label on alpha channel

[FFmpeg]

#6718: Option to remove label on alpha channel
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             Reporter:  ttdww        |                    Owner:
                 Type:  enhancement  |                   Status:  new
             Priority:  wish         |                Component:
              Version:  unspecified  |  undetermined
             Keywords:  alpha        |               Resolution:
             Blocking:               |               Blocked By:
Analyzed by developer:  0            |  Reproduced by developer:  0
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Comment (by ttdww):

 So sorry, I'm not sure. I'm just a graphics artist and CEO but not so much
 a coder.

 I only know that when a program (in this case FFmpeg) writes a Quicktime
 file from a string of 32bit images (.EXR, .TGA, or .PNG in this case), the
 alpha channel is usually in the input image string and then can be labeled
 when a Quicktime file is written, or left unlabeled.  There needs to be an
 option when writing the PNG 32bit QT file to leave the alpha 'unlabeled'.
 Currently FFmpeg sets the alpha in the QT file to 'straight' which most
 companies don't use when compositing for movies, games, TV, etc.

 The problem is that when a company like ours supplies them with hundreds
 of QT files, after the import of the first QT file, as long as the alpha
 is unlabeled they can choose the method they want: 'ignore alpha,
 straight, or premultiplied'.  Then the rest of the QT files will grab that
 default as they import.  If the alpha is already labeled (in the case of
 how FFmpeg currently writes them, it forces it to 'straight'), then the
 client will have to manually set each and every QT file to their
 preference, hence making the QT files not very usable.

 Thanks again!  Sorry, hope all that makes sense.  We're really hoping to
 ditch After Effects command-line processing and solely use FFmpeg if we
 could just get this resolved.

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Ticket URL: <https://trac.ffmpeg.org/ticket/6718#comment:10>
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