[FFmpeg-user] Cutting out part of a video does not work

[Peter White]

On Fri, Mar 26, 2021 at 07:02:13PM +0100, Cecil Westerhof via ffmpeg-user wrote:
> Carl Zwanzig <cpz at tuunq.com> writes:
> 
> > On 3/26/2021 9:28 AM, Cecil Westerhof via ffmpeg-user wrote:
> >> There is only one problem. The video is 7:21 long, but both mpv and
> >> vlc think it is 7:30 long.
> >
> > IME, the metadata length often lies. When you say it's 7:21, is that
> > exactly how long it plays for or how long it ought to be?
> 
> I almost never have this. (If I remember well, only with videos
> created with ffmpeg. Sometimes it started on a negative timestamp
> instead of 00:00:00.)
> 
> Looking at the -to you would expect 7:22, but when I just play it, it
> ends at 7:21.

You can try using -to as an input option as well. I am not sure, but I
seem to remember having similar problems once. Also, have a look at -t
for defining the length of the file as opposed to cutting on time code.

Plus, from your original post it looks like there is some additional
"data" stream in there, which might get copied. Sometime ffmpeg needs to
wait for that to finish or an opportune position to stop. Maybe that is
the culprit here. Have a look into the -map option, i.e. -map V -map a
should only give you video and audio but drop everything else.

> >> ffprobe version 4.1.6-1~deb10u1 Copyright (c) 2007-2020 the FFmpeg developers
> >
> > That's an older version, even though it wouldn't help on this, it's
> > always best to check with as current as you can get.
> 
> I am using Debian (stable). That always uses older versions.
> I could look if there is a newer version in backports.

You can compile it yourself as well. It is not that difficult. Might
need to hunt down some libraries, but that is basically just looking at
the error messages of configure and finding the appropriate packages.
Also, config.log and apt-file can help a great deal.


Cheers,
Peter