According to information I gathered, ffmpeg seeks internally using DTS
values instead of PTS. In some files DTS and PTS values are offset and
ffmpeg fails to seek correctly to keyframe located before requested PTS.
This issue become evident after hardcoded preseek of 25 frames was
removed and effort went into more precise seeking to improve
performance. It was thought, that this is bug in ffmpeg code, but
after reading some discussions, I don't think it is considered as such
by their developers, see below:
http://ffmpeg.org/pipermail/ffmpeg-devel/2018-March/226354.htmlhttps://trac.ffmpeg.org/ticket/1189
Best solution seems to be to add small preseek value possibly at
detriment of performance, so 3 frames of preseek are applied. Number 3
was chosen experimentally.
Performance impact seems to be insignificant with this change.
Reviewed By: zeddb
Differential Revision: https://developer.blender.org/D15847
bcc56253e2