[Bug 757933] New: When a pipeline is in GST_STATE_READY, "sync-message::need-context" is not emitted for GstGL.

[GStreamer (GNOME Bugzilla)]

https://bugzilla.gnome.org/show_bug.cgi?id=757933

            Bug ID: 757933
           Summary: When a pipeline is in GST_STATE_READY,
                    "sync-message::need-context" is not emitted for GstGL.
    Classification: Platform
           Product: GStreamer
           Version: 1.6.1
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: Normal
         Component: gst-plugins-bad
          Assignee: gstreamer-bugs at lists.freedesktop.org
          Reporter: changseok at gnome.org
        QA Contact: gstreamer-bugs at lists.freedesktop.org
     GNOME version: ---

This issue is found while testing yoon's experimental webkit branch
implementing GstGL support along with threaded compositor in webkitgtk+.
https://github.com/ryumiel/webkit-experimental/tree/threaded-compositor-wip

It works fine in overall, but there is some issues related with gstreamer.
How to reproduce.
1. Play a video and watch it completely.
2. Replay it in 60 secs.

When replaying a video, an unknown xwindow shows up of which name is "OpenGL
renderer". I have investigated it for a while, I found it was created by
gstreamer if no gl context is passed from the outside to the gstreamer at
beginning of the gst pipeline.
Of course webkit create a GstGL context and passes it to gst when listening the
"sync-message::need-context" signal from gstreamer.
The problem is that the singal is only emitted when the pipeline is in
GST_STATE_NULL, but not in GST_STATE_READY. I don't know why.
WebKit changes the pipeline state to GST_STATE_READY when receiving
GST_MESSAGE_EOS, and then changes it again to GST_STATE_NULL after 60 secs. As
I heard, this is due to better performance for replaying video.
Anyway if replaying video is triggered in the 60secs, the need-context signal
is not emitted so webkit can not create and pass a GstGL context for the new
gst pipeline and then it eventually leads gstreamer to create its own xwindow
along with a gl context. Replaying *after* 60secs is no problem.
So I think the best fix for this issue is that gstreamer emits
"sync-message::need-context" even in GST_STATE_READY so that it gives an
application a chance to create a gstgl context.
Any idea?

I'trying to make a test case for you though, I'm not a gst expert. So don't
believe me. :P (Of course, I'll provide you one if it is ready.)

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