[FFmpeg-devel] ffmpeg 4.4.6 2-pass null muxer segfault

[FFmpeg-devel] ffmpeg 4.4.6 2-pass null muxer segfault

[Elias Oenal via ffmpeg-devel]

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Hi,

I found this segfault when 2-pass x264 encoding a vfr file using ffmpeg
4.4.6 with the null muxer for the 1st pass. This results in a mismatch in
frames passed to x264, which in turn segfaults. I have submitted a patch to
x264 that allows it to gracefully activate a fallback, but 2-pass quality
will still be degraded. I am attaching an ffmpeg patch to warn the user and
exit when the situation is detected, but an alternative approach might be
to force CFR. Let me know what you prefer.

Please see the x264 PR for a minimal reproducer and debugger output:
https://code.videolan.org/videolan/x264/-/merge_requests/195

Best,
Elias

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