[FFmpeg-trac] #7883(ffmpeg:new): Videos with alpha channel are corrupted by scaling

FFmpeg trac at avcodec.org
Mon May 6 02:44:39 EEST 2019


#7883: Videos with alpha channel are corrupted by scaling
-------------------------------------+-------------------------------------
             Reporter:  Acru         |                     Type:  defect
               Status:  new          |                 Priority:  normal
            Component:  ffmpeg       |                  Version:  git-
             Keywords:  scale alpha  |  master
  regression                         |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug:

 When using the scale filter on a video with an alpha channel, or if the
 format is changed to rgba etc, the video is corrupted.  I have not checked
 if other filters are also effected.

 This issue appeared between build 20190312-d227ed5-win64-static and build
 ffmpeg-20190315-def18ac-win64-static, narrowing down what commit caused,
 though I am uncertain exactly which.  The issue persists in the latest
 build available to me, 20190505-e384f6f-win64-static

 How to reproduce:
 {{{
 A command such as the following, on a video with alpha;

 ffmpeg -i "Door (png).mov" -vf "scale=iw*0.5:-1" -y out.mp4

 Or any video when the format is changed to rgba;

 ffmpeg -i in.mp4 -vf "format=rgba,scale=iw*0.5:-1" -y out.mp4

 The output log does not indicate any differences, before and after the bug
 was introduced.
 }}}

 Some alpha-channeled videos are available here, for testing;
 https://drive.google.com/open?id=0Bxp60P6x4uM2clU3VF91bzlYMnc

--
Ticket URL: <https://trac.ffmpeg.org/ticket/7883>
FFmpeg <https://ffmpeg.org>
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