[FFmpeg-trac] #9531(undetermined:new): Unexpected ghosting around a transparent video encoded with hevc_videotoolbox

FFmpeg trac at avcodec.org
Thu Nov 25 12:35:31 EET 2021

#9531: Unexpected ghosting around a transparent video encoded with
             Reporter:  Chris        |                     Type:  defect
  Patuzzo                            |
               Status:  new          |                 Priority:  normal
            Component:               |                  Version:  git-
  undetermined                       |  master
             Keywords:  hevc         |               Blocked By:
  hevc_videotoolbox apple            |
  transparent alpha                  |
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
 '''Summary of the bug:'''

 I am trying to convert two transparent videos from VP9 to HEVC so that I
 can play them in Safari. They are both videos of some particle effects.
 The first video that contains black pixels transcodes correctly. The
 second video that contains blue pixels transcodes incorrectly. The alpha
 values around the edges of the particles seems to be incorrect creating a
 ghosting effect.

 The video with blue particles was generated from the one with black
 particles. I did this by mapping over each of the PNG files that were used
 to create the videos and re-mapping the color from black to blue. I
 believe I did this correctly. I can have attached one sample PNG of blue
 and black to this ticket.

 '''How to reproduce:'''

 This transcode produces the correct result:
 ffmpeg -c:v libvpx-vp9 -i black_particles.webm -c:v hevc_videotoolbox
 -alpha_quality 1 -vtag hvc1 black_particles.mov

 This transcode produces an incorrect result:
 ffmpeg -c:v libvpx-vp9 -i blue_particles.webm -c:v hevc_videotoolbox
 -alpha_quality 1 -vtag hvc1 blue_particles.mov

 I have attached the '-report -v 9 -loglevel 99' output for both transcodes
 as well as the input/output videos and screenshots that show the correct
 and incorrect ghosting in Apple's video preview.

 '''Build information:'''

 I built ffmpeg yesterday from the master branch, commit
 7e9e2cf93b6e22eaec72837ab59ac654c19b8d99. I used these parameters:

 ./configure --enable-libfdk-aac --enable-libvpx --enable-libvorbis
 --enable-libx265 --enable-libx264 --enable-gpl --enable-nonfree

 Many thanks
Ticket URL: <https://trac.ffmpeg.org/ticket/9531>
FFmpeg <https://ffmpeg.org>
FFmpeg issue tracker

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