Dynamic pipelines & gst_element_sync_state_with_parent() usage

[Stirling Westrup]

I'm currently struggling with a very similar issue. I have a dynamic
pipeline that is built during the pipeline transition from READY to
PAUSED state. During the transition decodebin produces output pad
depending on the input streams it finds. I have a callback that
attaches a video output bin to any video pads that appear, and an
audio output bin to any audio pads.

The trouble I have is that I need to pick up the video caps from the
end of the video processing bin, as it can have any number of video
rotating or resizing elements, depending on what the user put on the
command line.

Simply put, a probe I put on the video bin's output pad never sees any
fixed caps before the pipeline completes its transition to the PAUSED
state. However, when I tested this with a non-dynamic pipeline, it
worked.

So, how do I ensure that adding a bin to the pipeline during a state
transition will have it get fully synced with the rest of the
pipeline?  I've tried requesting the video bin to sync with parent
both before and after linking it to the decoder, and have had no luck
at all.

I'm beginning to think I'll need to capture a caps event from before
I've added the video processing bin, and then manually feed it through
the bin once I've put it in the pipeline.




On Tue, Jan 8, 2013 at 4:55 AM, Paddy <pat.blanchon at gmail.com> wrote:
> Hi All,
>
> I'm using gstreamer-0.10.
>
> I'm debugging some strange behaviour in my audio/video recording pipeline
> which saves to files in 30sec chunks & I've come across something that I
> need clearing up.
>
> When I create the new mux/filesink to record to I follow the accepted wisdom
> of:
> 1) create bin
> 2) add bin to parent
> 3) sync bin with parent using gst_element_sync_state_with_parent()
> 4) link bin to parent
> 5) unblock blocked pads
>
> The manual for  gst_element_sync_state_with_parent()
> <http://gstreamer.freedesktop.org/data/doc/gstreamer/0.10.36/gstreamer/html/GstElement.html#gst-element-sync-state-with-parent>
> states:
> "Returns : TRUE, if the element's state could be synced to the parent's
> state. MT safe."
>
> however looking at the code, it returns TRUE if the call to
> gst_element_set_state() does not return GST_STATE_CHANGE_FAILURE; AFAIK
> should the state change be asynchronous then there is no guarantee that the
> element is synced when TRUE is returned.
>
> So my question is:
> Do I need to wait for the state change to complete before linking (by
> creating a gst_element_really_sync_state_with_parent() function, say) ?
> or
> Is there some unwritten rule deep down in the code that makes the above a
> non-issue, & the child is synced with the parent before the link ?
>
> Cheers,
>
> Paddy
>
>
>
>
>
> --
> View this message in context: http://gstreamer-devel.966125.n4.nabble.com/Dynamic-pipelines-gst-element-sync-state-with-parent-usage-tp4657809.html
> Sent from the GStreamer-devel mailing list archive at Nabble.com.
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-- 
Stirling Westrup
Programmer, Entrepreneur.
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