Fix a deadlock when changing the video output

Changing the videooutput and deleting the mediaplayer
directly afterwards could lead to a deadlock, as the
videosink was blocking on a pad and then calling
a slot on the main thread using a blocking queued
connection. If the main thread was changing the state of
the gst pipeline at the same time, this could lead to
a deadlock.

Avoid it by pausing the pipeline before changing the
video output.

Change-Id: I0d0cbad0ab97a4eb83dd3c66c664c01de3b0ea90
Reviewed-by: Doris Verria <doris.verria@qt.io>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

1 files changed, 5 insertions, 0 deletions

diff --git a/src/multimedia/platform/gstreamer/common/qgstreamervideooutput.cpp b/src/multimedia/platform/gstreamer/common/qgstreamervideooutput.cpp
index f9bf9f6c2..982cdfc9c 100644
--- a/src/multimedia/platform/gstreamer/common/qgstreamervideooutput.cpp
+++ b/src/multimedia/platform/gstreamer/common/qgstreamervideooutput.cpp
@@ -80,7 +80,12 @@ void QGstreamerVideoOutput::setVideoSink(QVideoSink *sink)
     if (m_videoWindow) {
         connect(m_videoWindow, SIGNAL(sinkChanged()), this, SLOT(sinkChanged()));
     }
+    auto state = gstPipeline.state();
+    if (state == GST_STATE_PLAYING)
+        gstPipeline.setStateSync(GST_STATE_PAUSED);
     sinkChanged();
+    if (state == GST_STATE_PLAYING)
+        gstPipeline.setState(GST_STATE_PLAYING);
 }
 
 void QGstreamerVideoOutput::setPipeline(const QGstPipeline &pipeline)