gst-launch error handling

[Florian Lindner]

Hello,

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:


florian@horus ~/testconv % gst-launch-0.10 filesrc
location=accept.flac ! decodebin ! audioconvert ! lamemp3enc ! xingmux
! id3v2mux ! filesink location=out.mp3
Setting pipeline to PAUSED ...
Pipeline is PREROLLING ...
Redistribute latency...
Pipeline is PREROLLED ...
Setting pipeline to PLAYING ...
New clock: GstSystemClock
ERROR: from element
/GstPipeline:pipeline0/GstDecodeBin:decodebin0/GstFlacDec:flacdec0:
Could not decode stream.
Additional debug info:
gstflacdec.c(666): gst_flac_dec_error_cb ():
/GstPipeline:pipeline0/GstDecodeBin:decodebin0/GstFlacDec:flacdec0:
unknown error (3)
Execution ended after 11017569 ns.
Setting pipeline to PAUSED ...
Setting pipeline to READY ...
Setting pipeline to NULL ...
Freeing pipeline ...


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?

Thanks,

Florian
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[Tim-Philipp Müller-2]

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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[Florian Lindner]

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.

Regards,
Florian


2011/12/14 Tim-Philipp Müller <[hidden email]>:

> 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
>
> _______________________________________________
> gstreamer-devel mailing list
> [hidden email]
> http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel

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[Tim-Philipp Müller-2]

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 <[hidden email]>:
> > 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
> >
> > _______________________________________________
> > gstreamer-devel mailing list
> > [hidden email]
> > http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel
> _______________________________________________
> gstreamer-devel mailing list
> [hidden email]
> http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel

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[Florian Lindner]

2011/12/14 Tim-Philipp Müller <[hidden email]>:

> 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"

Ok, based on your code I created:


import gst

pipe_desc = "filesrc location=accept.flac ! decodebin ! audioconvert !
lamemp3enc ! xingmux ! id3v2mux ! filesink location=out.mp3"

pipeline = gst.parse_launch(pipe_desc)
print pipeline
bus = pipeline.get_bus()
print bus
msg = bus.poll(gst.MESSAGE_EOS | gst.MESSAGE_ERROR, -1)
print msg

timed_pop seems to be existing somewhere, but I was unable to find
documentation on it.
The code blocks forever at bus.poll and creates no output file:

florian@horus ~/testconv % python2 gsttest.py
** Message: pygobject_register_sinkfunc is deprecated (GstObject)
/GstPipeline:pipeline0 (gst.Pipeline)
/GstBus:bus2 (gst.Bus)

gst-launch $pipe_desc works as intended.

Any ideas?

Thanks!
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[Tim-Philipp Müller-2]

On Wed, 2011-12-14 at 14:49 +0100, Florian Lindner wrote:

> Ok, based on your code I created:
>
>
> import gst
>
> pipe_desc = "filesrc location=accept.flac ! decodebin ! audioconvert !
> lamemp3enc ! xingmux ! id3v2mux ! filesink location=out.mp3"
>
> pipeline = gst.parse_launch(pipe_desc)
> print pipeline
> bus = pipeline.get_bus()
> print bus
> msg = bus.poll(gst.MESSAGE_EOS | gst.MESSAGE_ERROR, -1)
> print msg
>
> timed_pop seems to be existing somewhere, but I was unable to find
> documentation on it.
> The code blocks forever at bus.poll and creates no output file:

You'll also have to set the pipeline to playing state before doing the
poll(), with pipeline.set_state(gst.STATE_PLAYING) or so.

Cheers
 -Tim

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[Florian Lindner]

Ok, it works this way now, Thanks!

One more question: On a successful convert I get a None Message:

(Pdb) msg
<gst.Message (none) from pipeline0 at 0x18e2080>

Stupid question... but how do I actually test for that message?

Florian

2011/12/14 Tim-Philipp Müller <[hidden email]>:

> On Wed, 2011-12-14 at 14:49 +0100, Florian Lindner wrote:
>
>> Ok, based on your code I created:
>>
>>
>> import gst
>>
>> pipe_desc = "filesrc location=accept.flac ! decodebin ! audioconvert !
>> lamemp3enc ! xingmux ! id3v2mux ! filesink location=out.mp3"
>>
>> pipeline = gst.parse_launch(pipe_desc)
>> print pipeline
>> bus = pipeline.get_bus()
>> print bus
>> msg = bus.poll(gst.MESSAGE_EOS | gst.MESSAGE_ERROR, -1)
>> print msg
>>
>> timed_pop seems to be existing somewhere, but I was unable to find
>> documentation on it.
>> The code blocks forever at bus.poll and creates no output file:
>
> You'll also have to set the pipeline to playing state before doing the
> poll(), with pipeline.set_state(gst.STATE_PLAYING) or so.
>
> Cheers
>  -Tim
>
> _______________________________________________
> gstreamer-devel mailing list
> [hidden email]
> http://lists.freedesktop.org/mailman/listinfo/gstreamer-devel

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