Public bug reported:
Hi,
after upgrading from ubuntu 16.04 with avconv to 18.04 with ffmpeg I
noticed that under certain conditions ffmpeg creates videos where the
video and audio get severely out of sync. It happens when using -c:v
copy and -ss before -i. See the attached Makefile to have a
demonstration of the problem.
As far as I can see this is releated to a new feature recently invented
in ffmpeg, where the precise jump should work as good as a skip.
Please notice: -ss before -i means seek in the source file, which is
fast, but said to be not working exact, but this was meant to be fixed,
and it meant that you don't get a precise cut, but audio + video still
in sync. It's extremely fast.
-ss after -i means to decode the source completely and to skip what's not
needed, which can become very slow. If you want to skip to a position at
2:00:00 you have to decode full two hours of video.
I tried to report the problem upstream, but they replied that a) they
ignore all bug reports not targeted to their git head version, and b)
with their head version they could not reproduce the problem. So it
seems to be fixed in newer version.
regards
ProblemType: Bug
DistroRelease: Ubuntu 18.04
Package: ffmpeg 7:3.4.2-2
ProcVersionSignature: Ubuntu 4.15.0-23.25-generic 4.15.18
Uname: Linux 4.15.0-23-generic x86_64
NonfreeKernelModules: zfs zunicode zavl icp zcommon znvpair
ApportVersion: 2.20.9-0ubuntu7.2
Architecture: amd64
CurrentDesktop: LXDE
Date: Wed Jul 18 11:17:20 2018
InstallationDate: Installed on 2018-04-30 (78 days ago)
InstallationMedia: Lubuntu 18.04 LTS "Bionic Beaver" - Release amd64 (20180426)
SourcePackage: ffmpeg
UpgradeStatus: No upgrade log present (probably fresh install)
** Affects: ffmpeg (Ubuntu)
Importance: Undecided
Status: New
** Tags: amd64 apport-bug bionic
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https://bugs.launchpad.net/bugs/1782323
Title:
-c:v copy renders audio and video out of sync
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