[FFmpeg-devel] multithreading hwaccel is broken on 5.1 and master branch

[Wang Bin]

cc867f2c09d2b69cee8a0eccd62aff002cbbfe11 this change breaks hwaccel. The
assertion av_assert0(!p->parent->stash_hwaccel) fails when seeking. So this
makes video players unusable. videotoolbox has another crash when starting
to decode. The crash can be reproduce easily in ffmpeg:
./ffmpeg -stream_loop -1 -an -hwaccel vaapi test.mp4 -f null - >/dev/null

Regards