[FFmpeg-devel] [PATCH] ffmpeg: modify tty state when stderr is redirected

Ganesh Ajjanagadde gajjanag at mit.edu
Mon Aug 3 16:34:22 CEST 2015

On Sat, Aug 1, 2015 at 6:54 AM, Nicolas George <george at nsup.org> wrote:
> Le quartidi 14 thermidor, an CCXXIII, Michael Niedermayer a écrit :
>> > ffmpeg -lavfi testsrc -f framecrc | head
>> Thats interresting, i tried this and it did not trash my terminal
>> also ive almost never seen ffmpeg trash my terminal with the current
>> code. No matter how i run it
> As Ganesh noticed, I forgot the output "-" in my example, but you probably
> noticed that on your own, and that is not the issue.
> I just ran some tests and it appears that bash restores the tty state if the
> command was killed by a signal but not if it exited normally.
> Therefore, "ffmpeg ... - | head" will have the tty restored because ffmpeg
> dies by SIGPIPE, but "strace ffmpeg ... - | head" will trash the tty state
> because bash does not know of the SIGPIPE. The same goes for anything that
> runs ffmpeg as a sub-process, from "sh -c ..." to the FATE harness.
> Well, bash does part of its job, but I consider it should do more: leaving
> the tty trashed just because you inserted strace in front of the command is
> bad policy.

Above example shows that even without this patch, tty state can be trashed.
Thus tty trashing is unavoidable, and only fix for this is via shell
configuration (see patch 2/3).
Therefore this patch should be included to fix Ticket2964.

> Regards,
> --
>   Nicolas George
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