From: Elias Oenal via ffmpeg-devel <ffmpeg-devel@ffmpeg.org>
To: ffmpeg-devel@ffmpeg.org
Cc: Elias Oenal <ffmpeg@eliasoenal.com>
Subject: [FFmpeg-devel] ffmpeg 4.4.6 2-pass null muxer segfault
Date: Fri, 6 Feb 2026 15:22:51 -0800
Message-ID: <CACUTcScZSKAO=1n_XdPcMAXPjTVN3XJ_ckeCjnx0mvVy3-SKHA@mail.gmail.com> (raw)
[-- Attachment #1: Type: text/plain, Size: 638 bytes --]
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
[-- Attachment #2: 0001-ffmpeg-detect-vfr-2pass-null-muxer-mismatch.patch --]
[-- Type: application/octet-stream, Size: 1790 bytes --]
[-- Attachment #3: Type: text/plain, Size: 163 bytes --]
_______________________________________________
ffmpeg-devel mailing list -- ffmpeg-devel@ffmpeg.org
To unsubscribe send an email to ffmpeg-devel-leave@ffmpeg.org
reply other threads:[~2026-02-06 23:23 UTC|newest]
Thread overview: [no followups] expand[flat|nested] mbox.gz Atom feed
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to='CACUTcScZSKAO=1n_XdPcMAXPjTVN3XJ_ckeCjnx0mvVy3-SKHA@mail.gmail.com' \
--to=ffmpeg-devel@ffmpeg.org \
--cc=ffmpeg@eliasoenal.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Git Inbox Mirror of the ffmpeg-devel mailing list - see https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
This inbox may be cloned and mirrored by anyone:
git clone --mirror https://master.gitmailbox.com/ffmpegdev/0 ffmpegdev/git/0.git
# If you have public-inbox 1.1+ installed, you may
# initialize and index your mirror using the following commands:
public-inbox-init -V2 ffmpegdev ffmpegdev/ https://master.gitmailbox.com/ffmpegdev \
ffmpegdev@gitmailbox.com
public-inbox-index ffmpegdev
Example config snippet for mirrors.
AGPL code for this site: git clone https://public-inbox.org/public-inbox.git