[FFmpeg-trac] #2275(FFplay:closed): artifacts on decoding PNG file with alpha

[FFmpeg]

#2275: artifacts on decoding PNG file with alpha
---------------------------------------+-----------------------------------
             Reporter:  saste          |                    Owner:
                 Type:  defect         |                   Status:  closed
             Priority:  normal         |                Component:  FFplay
              Version:  git-master     |               Resolution:  invalid
             Keywords:  png alpha sdl  |               Blocked By:
             Blocking:                 |  Reproduced by developer:  1
Analyzed by developer:  1              |
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Changes (by saste):

 * analyzed:  0 => 1
 * keywords:  png alpha => png alpha sdl
 * status:  open => closed
 * component:  avcodec => FFplay
 * resolution:   => invalid


Comment:

 Replying to [comment:2 cehoyos]:
 > Is there really an issue?
 > ImageMagick decodes exactly the same (invisible) artefacts as FFmpeg.

 Indeed it isn't.
 {{{
 ffplay -f lavfi "color=s=400x300:c=white[bg]; movie=ffmpeg-logo.png, [bg]
 overlay"
 }}}

 or
 {{{
 ffplay ffmpeg-logo.png -vf alphaextract
 }}}

 libswscale is stripping the alpha plane when converting from RGBA to YUV,
 and the display is the natural result of this operation, the only sane
 path would be to make the output device support alpha, but this is
 unrelated to FFmpeg.

 Sorry for the noise.

-- 
Ticket URL: <https://ffmpeg.org/trac/ffmpeg/ticket/2275#comment:3>
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