Dynamic pipeline

[Haakon Sporsheim]

Hi

I'm working on a product that uses GStreamer for real time communication
(read: VoIP). We started out using GStreamer 0.10 a couple of years ago,
and now have ported our elements to 1.0.

For GStremer 0.10 we developed a pretty large test suite for testing and
stressing both stock GStreamer elements and our own to check that they are
'compliant' (or at least doesn't crash, leak or does stupid things). Some
of these tests used a test tool called GstHarness [1] that was presented by
Håvard Graff at GStreamer conference 2013 [2].
This tool basically starts some threads which all prod an element or a set
of elements. An example would be pushing buffers in one thread, sending
events in the second and changing state in the third.

After porting this to GStreamer 1.0 this is somewhat harder because of the
requirement of GST_EVENT_START_STREAM and GST_EVENT_SEGMENT being present
before data flow. Going to GST_STATE_NULL will deactivate its pads, which
again will remove all sticky events.
I've found that if a buffer is on its way between two elements and pads in
a streaming thread; the downstream element goes to GST_STATE_NULL then up
again to GST_STATE_PLAYING in an application thread, it will not have any
sticky events and you'll get the g_warning: "Got data flow before
stream-start event".

I guess this is a very unlikely scenario for a real life pipeline, but I'd
like to get someones view on it. Is this something that should work? Should
it be possible to pick out an element in a pipeline, take the element down
in state, then up again and expect everything to just proceed as normal
after that?

I'll try to get some time later this week to add a test case to
prove/showcase what I'm trying to describe here without the use of
GstHarness.

Thanks, Best Regards,
Haakon Sporsheim (ieei on #gstreamer)

[1] https://github.com/pexip/gstreamer/commits/
[2]
http://gstconf.ubicast.tv/videos/achieving-pexcellence-challenges-of-real-time-streaming-applications/
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