[FFmpeg-trac] #8655(ffmpeg:new): Crash with kmsgrab, vaapi_scale and hwdownload

[FFmpeg]

#8655: Crash with kmsgrab, vaapi_scale and hwdownload
-------------------------------------+-------------------------------------
             Reporter:               |                     Type:  defect
  0x53ee71ebe11e                     |
               Status:  new          |                 Priority:  normal
            Component:  ffmpeg       |                  Version:  git-
                                     |  master
             Keywords:               |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 While trying to figure out another problem (#8377, may or may not be
 related), I came upon this crash:

 {{{
 ffmpeg_g -v 9 -loglevel 99 -f kmsgrab -framerate 60 -i - -map 0 -vf
 'hwmap=derive_device=vaapi,scale_vaapi=960:540,hwdownload,format=bgr0'
 -c:v h264 -preset veryfast /tmp/output.mp4
 }}}

 I changed the command line from over in that other ticket. The idea was to
 skip the hardware encoder and use the software encoder instead after
 scaling down the source on the gpu. And I was greeted with a crash. See
 attachement.

 Leaving out the scale_vaapi filter works without crash.

 I am not sure if using scale_vaapi without using the vaapi encoder
 afterwards is even a valid thing to do, but it shouldn't crash no matter
 what.

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Ticket URL: <https://trac.ffmpeg.org/ticket/8655>
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