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up vote 2 down vote favorite

So I have a line here that is meant to dump frames from a movie via python and ffmpeg.

subprocess.check_output([ffmpeg, "-i", self.moviefile, "-ss 00:01:00.000 -t 00:00:05 -vf scale=" + str(resolution) + ":-1 -r", str(framerate), "-qscale:v 6", self.processpath + "/" + self.filetitles + "-output%03d.jpg"])

And currently it's giving me the error:

'CalledProcessError: Command ... returned non-zero exit status 1'

The command python SAYS it's running is:

'['/var/lib/openshift/id/app-root/data/programs/ffmpeg/ffmpeg', '-i', u'/var/lib/openshift/id/app-root/data/moviefiles/moviename/moviename.mp4', '-ss 00:01:00.000 -t 00:00:05 -vf scale=320:-1 -r', '10', '-qscale:v 6', '/var/lib/openshift/id/app-root/data/process/moviename/moviename-output%03d.jpg']'

But when I run the following command via ssh...

'/var/lib/openshift/id/app-root/data/programs/ffmpeg/ffmpeg' -i '/var/lib/openshift/id/app-root/data/moviefiles/moviename/moviename.mp4' -ss 00:01:00.000 -t 00:00:05 -vf scale=320:-1 -r 10 -qscale:v 6 '/var/lib/openshift/id/app-root/data/process/moviename/moviename-output%03d.jpg'

It works just fine. What am I doing wrong? I think I'm misunderstanding the way subprocess field parsing works...

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2 Answers 2

up vote 2 down vote accepted

The subprocess module doesn't allow any whitespace characters in its parameters, unless you run it in shell mode. Try this:

subprocess.check_output(["ffmpeg", "-i", self.moviefile, "-ss", "00:01:00.000", "-t", "00:00:05", "-vf", "scale=" + str(resolution) + ":-1", "-r", str(framerate), "-qscale:v", "6", self.processpath + "/" + self.filetitles + "-output%03d.jpg"])
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That's exactly the problem I had with convert (imagemagick) –  Steve K 1 hour ago
    
Thanks so much! This is a clear explanation =D –  Varda Elbereth 1 hour ago
up vote 1 down vote

The argument array you pass to check_call is not correctly formatted. Every arguent to ffmpeg needs to be a single element in the argument list, for example

... "-ss 00:01:00.000 -t 00:00:05 -vf ...

should be

... "-ss", "00:01:00.000", "-t", "00:00:05", "-vf", ...

The complete resulting args array should be:

['ffmpeg', '-i', '/var/lib/openshift/id/app-root/data/moviefiles/moviename/moviename.mp4', '-ss', '00:01:00.000', '-t', '00:00:05', '-vf', 'scale=320:-1', '-r', '10', '-qscale:v', '6', '/var/lib/openshift/id/app-root/data/process/moviename/moviename-output%03d.jpg']
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