[gst-devel] Start recording from a webcam already playing

[Marc]

Thank you very much Arnout.

Using the method you described I am able to record from the webcam every
time the user presses a button. As you pointed, also, I am having trouble
with timestamps. In my case, since I just need to record one file at time, I
would be ok to reset the base time for the v4l2src element. However ,when I
try to set the base_time to 0 for this element it stops streaming new
images.

Since I'd like to stick to the "default" gstreamer packages, is there a way
to set the base_time for v4l2src without it being stopped ?

Thanks

2009/1/31 Arnout Vandecappelle <arnout at mind.be>

> On Friday 30 January 2009 20:37:49 Marc wrote:
> > I am trying to build an application more or less like Cheese
> > (http://projects.gnome.org/cheese/). However I would like to switch from
> > just showing the webcam to a recording state "smoothly" when the user
> press
> > the record button.
> >
> > So far I have tried the following approaches without succes:
> > Changing location property of filesink while playing (from /dev/null to a
> > real path). This is not possible (filesink tells me so). Open 2 different
> > pipelines both of them pointing to the same v4l2src (no success since
> only
> > one pipeline can access the webcam at once). Since these approaches were
> > not working I tried to set the pipeline to STATE_NULL, change the
> location
> > of the filesink, and then set the pipeline to STATE_PLAYING again.
> However,
> > when setting the pipeline to STATE_NULL, no STATE_CHANGE event is thrown.
> > Is this the expected behavior ?
> >
> > Any ideas ? Can the smooth "play-to-record" be accomplished with
> GStreamer
> > ?
> >
> > Thank you
> > PD. For the record: I am programming in Python and the pipeline I am
> trying
> > to manage is the following:
> >
> >  gst-launch-0.10 v4l2src ! tee name=videoout ! queue ! videorate !
> > video/x-raw-yuv,fps=15 ! queue ! theoraenc quality=60 ! queue ! muxout.
> > pulsesrc ! audio/x-raw-int,rate=22000,channels=1,width=16 ! queue !
> > audioconvert ! vorbisenc ! queue ! muxout. oggmux name=muxout ! filesink
> > location=test.ogg videoout. ! queue ! ffmpegcolorspace ! ximagesink
>
>  You can add the videoout tail of the pipeline dynamically.  Start without
> it,
> and when the user presses the record button, add it to the pipeline and
> link
> it (and set each element to PLAYING individually).  It's not even necessary
> to pause the pipeline.
>
>  It's more difficult to smoothly stop the recording, though.  You'll have
> to
> block the queue element behind the tee (see docs/design/part-block.txt in
> the
> source tree).  In addition, you have to push an EOS into it to make sure
> the
> muxer writes duration and index to the file.
>
>  A last caveat is the timestamps.  The buffer timestamps start running as
> soon
> as the v4l2src starts playing, which makes it appear in the output file as
> if
> it starts with a big hole.  The only way I found to fix that is to add an
> adapter element that shifts the buffer timestamps (see
> http://bugzilla.gnome.org/show_bug.cgi?id=561224 ).
>
>  Regard,
>  Arnout
> --
> Arnout Vandecappelle                               arnout at mind be
> Senior Embedded Software Architect                 +32-16-286540
> Essensium/Mind                                     http://www.mind.be
> G.Geenslaan 9, 3001 Leuven, Belgium                BE 872 984 063 RPR
> Leuven
> LinkedIn profile: http://www.linkedin.com/in/arnoutvandecappelle
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>
>
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-- 
Marc S.
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