[FFmpeg-user] Python / Qprocess misfires commands.

Moritz Barsnick barsnick at gmx.net
Tue May 18 17:28:55 EEST 2021

On Tue, May 18, 2021 at 12:05:40 +0200, Bouke wrote:
> > Then you're capturing your output incorrectly.

> Nah, this was an apology for an earlier message where I ment ’nothing except the banner'

Hmm. Your attached reports indicate that there were more log messages.
I wonder where they went...

> > If QProcess terminates it unconditionally, there's nothing we can do(?).
> I understand, but now it’s the blame game, what happens where / when / why?

Sure. I don't understand QProcess (yet, or anymore), so I have no idea
what to debug. I don't know what to make of the return code 6 either.
it doesn't come from ffmpeg, as far as I can tell from the latter's

ffmpeg isn't stuck at that point, it just terminates, right?

> > If ffmpeg crashes, that's bad. You would have to convince your system
> > to create a core dump, and would have to look at a backtrace. (Or run
> > ffmpeg within gdb.)
> Eeh, I’m a simple scripter, not a coder, no clue how to do that...

(If you can operate QProcess, you're no longer a "simple" scripter.)

Well, if MacOS happens to have gdb, it would work by replacing your
ffmpeg command line with:

$ gdb -ex r -ex bt --args ffmpeg [further command line options]

i.e. prepending gdb. The ffmpeg binary should not be stripped for this
to work properly.

MacOS may have lldb instead of gdb, but I have no experience in
operating that.

> > Do you need to run it in bash? Can you not set cmd to "ffmpeg" and
> > properly pass the arguments?
> Normally I do that, especially as that saves tons of headaches on escaping stuff.
> But this was a suggestion from the QT forum, hoping it would provide a bit more insight.
> https://forum.qt.io/topic/126674/escaping-colon-in-command-line-argument/8 <https://forum.qt.io/topic/126674/escaping-colon-in-command-line-argument/8>
> Trust me, it makes no difference if I use separate args or run it as bash.

I trust you. I was just speculating.


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