[FFmpeg-trac] #10901(undetermined:new): HEVC with alpha to PNG does not maintain alpha

[FFmpeg]

#10901: HEVC with alpha to PNG does not maintain alpha
--------------------------------------+----------------------------------
             Reporter:  Jozef Chutka  |                     Type:  defect
               Status:  new           |                 Priority:  normal
            Component:  undetermined  |                  Version:  6.1
             Keywords:  Hevc alpha    |               Blocked By:
             Blocking:                |  Reproduced by developer:  0
Analyzed by developer:  0             |
--------------------------------------+----------------------------------
 When converting hevc.mp4 with alpha into PNG, the alpha information is not
 respected, producing opaque PNG.

 How to reproduce:

 {{{
 % ffmpeg -i hevc.mp4 -vframes 1 output.png
 }}}

 hevc.mp4 was created from source image with alpha channel and seems to
 have the alpha properly encoded:

 {{{
 ffmpeg -i source.png -vcodec hevc_videotoolbox -r 1 -t 1 -vtag hvc1
 -alpha_quality 1 -y hevc.mp4
 }}}

 Following https://trac.ffmpeg.org/ticket/7965 which refers to
 https://patchwork.ffmpeg.org/project/ffmpeg/patch/tencent_5F1F4DA9CFDF5521A752B8C9161A4D23A007@qq.com/
 it seems hevcdec has some kind of decoding support for alpha channel... is
 it hidden behind some command line flag?
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/10901>
FFmpeg <https://ffmpeg.org>
FFmpeg issue tracker