[FFmpeg-trac] #6256(undetermined:new): Showpalette filter returns default palette for GIF.

FFmpeg trac at avcodec.org
Thu Mar 23 16:39:26 EET 2017

#6256: Showpalette filter returns default palette for GIF.
             Reporter:  mulvya       |                    Owner:
                 Type:  defect       |                   Status:  new
             Priority:  normal       |                Component:
              Version:  git-master   |  undetermined
             Keywords:  gif          |               Resolution:
  regression                         |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
Changes (by cehoyos):

 * keywords:   => gif regression


 If there were an issue, this would be a regression since

 But FFmpeg does not guarantee to output a particular colour space for a
 given file (as it does not guarantee a particular audio sample format when
 decoding a given file), this behaviour isn't part of the API/ABI (this is
 why API users always have to check the pix_fmt and sample_fmts that
 encoders need / decoders provide). Note that decoding of the provided file
 only works since f83657fc, four commits  after the requested feature was
 "broken" / the reported "bug" was introduced.
 From FFmpeg's pov, the provided file is not palettized, to get a palette
 for the given (bgra) file, using the palettegen filter is required. Using
 the showpalette filter for a file that isn't palettized will show a
 default filter.

 Not closing yet as I don't know if changing the current behaviour of the
 gif decoder / demuxer is possible or not, this may be a valid feature

 For future tickets: Please do not provide output files unless specifically
 asked to, attaching them very often leads to confusion.

Ticket URL: <https://trac.ffmpeg.org/ticket/6256#comment:2>
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