Pause and resume live video with latest frames without affecting the sink

[Nicolas Dufresne]

Le mercredi 22 août 2018 à 10:33 -0500, vk_gst a écrit :
> Hi,
> 
> 
> > Shouldn't you set drop-probability=1 _after_ adding imagefreeze to let
> > it get at least one buffer to duplicate? 
> 
> I see I made a mistake here. I totally removed the identity element now. So
> the pipeline is 
> v4l2src -> queue -> h264parse ->avdec_h264 -> imagefreeze(dynamically
> added/removed) -> glupload -> glcolorconvert -> gltransformation ->
> glimagesink. 
> 
> With this pipeline, based on user input I add the imagefreeze element, and
> then I am able to apply gltransformation on the paused video frame.  For
> other input, I am removing the imagefreeze element from pipeline, and I hope
> to see the video replay again. But I observe the following error : 
> 
> 0:00:12.412324825 16939      0x2655b20 WARN             imagefreeze
> gstimagefreeze.c:851:gst_image_freeze_src_loop:<ifreeze> error: Internal
> data stream error.
> 0:00:12.412424980 16939      0x2655b20 WARN             imagefreeze
> gstimagefreeze.c:851:gst_image_freeze_src_loop:<ifreeze> error: streaming
> stopped, reason not-linked (-1)
> ERROR: ifreeze : Internal data stream error.
> debugging info: gstimagefreeze.c(851): gst_image_freeze_src_loop ():
> /GstPipeline:test-pipeline/GstImageFreeze:ifreeze:
> streaming stopped, reason not-linked (-1)
> 
> While removing the element imagefreeze, 
> 1. I send a EOS event as sink pad of imagefreeze,
> 2.  unlink src and sink pads of avdec_h264 and upload,
> 3.  set state to NULL, 
> 4. link back avdec_h264 and upload.

I don't think you have to care about draining imagefreeze. Though, this
is a bit more involving, since you have to use pad probes in order to
block the flow during the dynamic pipeline modification. As the time
will continue going forward with imagefreeze, you will also have to
tracked the elapsed time and find a way to offset the remaining. This
is a bit difficult, but doable.

> 
> 
> > Not sure if you have to decouple the pipeline, I've no direct
> > experience with that.
> 
> The point of adding and deleting element imagefreeze was taken from some
> earlier suggestions, so that I receive the last buffer and can apply
> gltransformation accordingly. 
> 
> > However from my intuitions this could solve two problems:
> > 
> > 1. you won't stall the pipeline
> > 
> > 2. you'd let imagefreeze still be able to get the last buffer when
> > you "pause" upstream.
> > For example, compare this pipeline:
> > gst-launch-1.0 videotestsrc ! \
> >               identity drop-probability=1 ! \
> >               imagefreeze ! \
> >               videoconvert ! rotate angle=10 ! videoconvert ! \
> >               fpsdisplaysink
> > With this pipeline:
> > gst-launch-1.0 videotestsrc ! \
> >               identity drop-probability=1 ! \
> >               intervideosink intervideosrc ! \
> >               imagefreeze ! \
> >               videoconvert ! rotate angle=10 ! videoconvert ! \
> >               fpsdisplaysink
> > The second one progresses (even though with drop-probability=1 set
> > from the beginning the last buffer is not passed to imagefreeze), while
> > the first one stalls.
> 
> I am not sure if I understand this 2 pipelines correctly.  I see no
> difference in the rendering video. Its complete black in both cases, and it
> should be since the identity has blocked the output. However in the second
> pipeline, the comments displayed after execution has an extra line :
> 'Pipeline is live and does not need PREROLL ...' . This is not seen when
> executing the first pipeline.
> 
> > If this works maybe you could even just pause the "src pipeline" in the
> > normal way without the identity hack.
> 
> 
> Regards,
> VK
> 
> 
> 
> --
> Sent from: http://gstreamer-devel.966125.n4.nabble.com/
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