gst-launch error handling

[Tim-Philipp Müller]

On Wed, 2011-12-14 at 13:08 +0100, Florian Lindner wrote:

> I feared that answer. I have already searched the web for a minimal
> python example. The "official" examples at
> http://pygstdocs.berlios.de/pygst-tutorial/index.html all involve a
> lot of GTK code for creating windows etc. I simply find no starting
> point with the python API. If I really need that mass of code (like in
> the aforementioned examples) for just duplicating that gst-launch
> call, I would rather go with executing gst-launch and parse the output
> for errors.

You don't need that much code (you didn't say whether it's ok to block
while waiting for the pipeline or finish or error out).

In the simplest case you can just do something like (pseudo-code):

  pipeline = gst.parse_launch("...")
  bus = pipeline.get_bus()
  msg=bus.timed_pop(gst.MESSSAGE_EOS | gst.MESSAGE_ERROR,
gst.CLOCK_TIME_NONE)
  if msg.type == gst.MESSAGE_ERROR:
    print "Error!"
  else:
    print "Done"

Feel free to submit a patch to fix up the exit code regardless, but
calling gst-launch like that in an application is just a bad idea.

 Cheers
  -Tim

> 
> 2011/12/14 Tim-Philipp Müller <t.i.m at zen.co.uk>:
> > On Wed, 2011-12-14 at 12:42 +0100, Florian Lindner wrote:
> >
> >> I plan to use gst-launch in a simple python script that mass converts
> >> flac to mp3 files. I would use it like that:
> >>
> >> gst-launch-0.10 filesrc location=accept.flac ! decodebin !
> >> audioconvert ! lamemp3enc ! xingmux ! id3v2mux ! filesink
> >> location=out.mp3
> >>
> >> How can I do error handling if any of the pipeline modules produce an
> >> error? e.g. I've modified the flac file to be invalid, that produces
> >> that output:
> >> ...
> >> Returncode is 0. How to detect an error? Parse output for ERROR?
> >>
> >> I know that gst-launch is not intended for applications, but in my
> >> simple case using the python interface with the event loop and all
> >> that stuff seems to be a bit too much. Or have I mistaken the API
> >> docs?
> >
> > If you have a python script, you should probably just use the gstreamer
> > python bindings and use pipeline = gst.parse_launch("....") and then
> > check for error message on the pipeline's bus (or EOS), either in a
> > blocking way (timed_pop) or asynchronously (running a main loop).
> >
> >  Cheers
> >  -Tim
> >
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