GStreamer: mark videosinks as "async"

`finishStateChange` and friends don't fully wait for the pipeline state
to be changed, since the sink elements is marked as async.
Therefore `gst_element_get_state` replies with `GST_STATE_CHANGE_ASYNC`.

This seems to have some side effects like crashes/deadlocks when
switching cameras or switching output sinks.

Fixes: QTBUG-122638
Fixes: QTBUG-123139
Fixes: QTBUG-113421
Pick-to: 6.5
Change-Id: I770aaec5c0f35b7aa9fd52c3484608b1c8114ba2
Reviewed-by: Artem Dyomin <artem.dyomin@qt.io>
(cherry picked from commit 6e0a706d907152a51c093cd37113c324d243d039)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit bc8ff8da8b952afd9e9607212f04e05fa39c36a7)

2 files changed, 7 insertions, 0 deletions

diff --git a/src/plugins/multimedia/gstreamer/common/qgstreamervideooutput.cpp b/src/plugins/multimedia/gstreamer/common/qgstreamervideooutput.cpp
index 66d5b4734..929375a0b 100644
--- a/src/plugins/multimedia/gstreamer/common/qgstreamervideooutput.cpp
+++ b/src/plugins/multimedia/gstreamer/common/qgstreamervideooutput.cpp
@@ -54,6 +54,10 @@ QGstreamerVideoOutput::QGstreamerVideoOutput(QGstElement convert, QGstElement sc
       videoSink(std::move(sink))
 {
     videoQueue = QGstElement::createFromFactory("queue", "videoQueue");
+
+    videoSink.set("sync", true);
+    videoSink.set("async", false); // no asynchronous state changes
+
     if (videoScale) {
         gstVideoOutput.add(videoQueue, videoConvert, videoScale, videoSink);
         qLinkGstElements(videoQueue, videoConvert, videoScale, videoSink);
@@ -91,6 +95,7 @@ void QGstreamerVideoOutput::setVideoSink(QVideoSink *sink)
         gstSink = QGstElement::createFromFactory("fakesink", "fakevideosink");
         Q_ASSERT(gstSink);
         gstSink.set("sync", true);
+        gstSink.set("async", false); // no asynchronous state changes
         isFakeSink = true;
     }
 
diff --git a/src/plugins/multimedia/gstreamer/common/qgstreamervideosink.cpp b/src/plugins/multimedia/gstreamer/common/qgstreamervideosink.cpp
index f3dc36271..7f7d9a49b 100644
--- a/src/plugins/multimedia/gstreamer/common/qgstreamervideosink.cpp
+++ b/src/plugins/multimedia/gstreamer/common/qgstreamervideosink.cpp
@@ -180,6 +180,8 @@ void QGstreamerVideoSink::updateSinkElement()
         if (!gstVideoSink.isNull())
             sinkBin.stopAndRemoveElements(gstVideoSink);
 
+        newSink.set("async", false); // no asynchronous state changes
+
         gstVideoSink = newSink;
         sinkBin.add(gstVideoSink);
         qLinkGstElements(gstCapsFilter, gstVideoSink);