[FFmpeg-user] How to preserve file time

[Nicolas George]

Oliver Fromme (12024-08-21):
> I'm sorry this mail is going to be rather long.  However, I would
> like to explain my opinion on this matter in detail.

You are more patient than this issue deserves.

> In fact, I can rather imagine use cases to preserve the *atime*
> (access time) of the input files, rather than overriding the mtime
> of output files.  So, in my opinion, an option to reset the atime
> when FFmpeg is finished would be more useful (and it would be much
> easier to implement).  But I wouldn't propose it either, because it
> can be trivially done with an OS command, too.

That is not entirely true.

*Restoring* the atime can easily be done with an OS command, but it is an
aberration that will trigger an update to the ctime. Do not do that.

*Preserving* the atime cannot be done with a simple OS command, it
requires a flag on the open() system call (and corresponding
permission).

rsync has the option:

       --open-noatime
              This  tells rsync to open files with the O_NOATIME flag (on sys‐
              tems that support it) to avoid changing the access time  of  the
              files  that  are being transferred.  If your OS does not support
              the O_NOATIME flag then rsync will silently ignore this  option.
              Note  also  that  some filesystems are mounted to avoid updating
              the atime on read access even without the O_NOATIME  flag  being
              set.

But rsync is a synchronization tool, and synchronizing without altering
is a very important feature.

> (*)  Well, in theory you can use FFmpeg to make a 1:1 copy (-map 0,
> same container), but even then details will usually be different

Add -f data and you will have an exact binary copy.

Regards,

-- 
  Nicolas George