GStreamer: flush the current frame when stopping a media player.

When stopping, we don't actually stop the GStreamer pipeline, we just
pause it and prevent preroll frames from being shown.
We also need to make sure the last presented frame is cleared in that
case, otherwise it stays on screen.
Fixed for both 0.10 and 1.0.

Change-Id: Ibe26a7567f271ae0c3d8819eb9d35d6a95da1c6a
Reviewed-by: Christian Stromme <christian.stromme@theqtcompany.com>

src/gsttools/qgstvideorenderersink.cpp

@@ -222,6 +222,17 @@ bool QVideoSurfaceGstDelegate::proposeAllocation(GstQuery *query)
     }
 }
 
+void QVideoSurfaceGstDelegate::flush()
+{
+    QMutexLocker locker(&m_mutex);
+
+    m_flush = true;
+    m_renderBuffer = 0;
+    m_renderCondition.wakeAll();
+
+    notify();
+}
+
 GstFlowReturn QVideoSurfaceGstDelegate::render(GstBuffer *buffer)
 {
     QMutexLocker locker(&m_mutex);
@@ -388,6 +399,8 @@ QGstVideoRendererSink *QGstVideoRendererSink::createSink(QAbstractVideoSurface *
 
     sink->delegate = new QVideoSurfaceGstDelegate(surface);
 
+    g_signal_connect(G_OBJECT(sink), "notify::show-preroll-frame", G_CALLBACK(handleShowPrerollChange), sink);
+
     return sink;
 }
 
@@ -472,13 +485,41 @@ void QGstVideoRendererSink::finalize(GObject *object)
     G_OBJECT_CLASS(sink_parent_class)->finalize(object);
 }
 
+void QGstVideoRendererSink::handleShowPrerollChange(GObject *o, GParamSpec *p, gpointer d)
+{
+    Q_UNUSED(o);
+    Q_UNUSED(p);
+    QGstVideoRendererSink *sink = reinterpret_cast<QGstVideoRendererSink *>(d);
+
+    gboolean showPrerollFrame = true; // "show-preroll-frame" property is true by default
+    g_object_get(G_OBJECT(sink), "show-preroll-frame", &showPrerollFrame, NULL);
+
+    if (!showPrerollFrame) {
+        GstState state = GST_STATE_VOID_PENDING;
+        gst_element_get_state(GST_ELEMENT(sink), &state, NULL, GST_CLOCK_TIME_NONE);
+        // show-preroll-frame being set to 'false' while in GST_STATE_PAUSED means
+        // the QMediaPlayer was stopped from the paused state.
+        // We need to flush the current frame.
+        if (state == GST_STATE_PAUSED)
+            sink->delegate->flush();
+    }
+}
+
 GstStateChangeReturn QGstVideoRendererSink::change_state(
         GstElement *element, GstStateChange transition)
 {
-    Q_UNUSED(element);
+    QGstVideoRendererSink *sink = reinterpret_cast<QGstVideoRendererSink *>(element);
 
-    return GST_ELEMENT_CLASS(sink_parent_class)->change_state(
-            element, transition);
+    gboolean showPrerollFrame = true; // "show-preroll-frame" property is true by default
+    g_object_get(G_OBJECT(element), "show-preroll-frame", &showPrerollFrame, NULL);
+
+    // If show-preroll-frame is 'false' when transitioning from GST_STATE_PLAYING to
+    // GST_STATE_PAUSED, it means the QMediaPlayer was stopped.
+    // We need to flush the current frame.
+    if (transition == GST_STATE_CHANGE_PLAYING_TO_PAUSED && !showPrerollFrame)
+        sink->delegate->flush();
+
+    return GST_ELEMENT_CLASS(sink_parent_class)->change_state(element, transition);
 }
 
 GstCaps *QGstVideoRendererSink::get_caps(GstBaseSink *base, GstCaps *filter)

src/gsttools/qvideosurfacegstsink.cpp

@@ -184,6 +184,21 @@ void QVideoSurfaceGstDelegate::clearPoolBuffers()
         m_pool->clear();
 }
 
+void QVideoSurfaceGstDelegate::flush()
+{
+    QMutexLocker locker(&m_mutex);
+
+    m_frame = QVideoFrame();
+    m_renderCondition.wakeAll();
+
+    if (QThread::currentThread() == thread()) {
+        if (!m_surface.isNull())
+            m_surface->present(m_frame);
+    } else {
+        QMetaObject::invokeMethod(this, "queuedFlush", Qt::QueuedConnection);
+    }
+}
+
 GstFlowReturn QVideoSurfaceGstDelegate::render(GstBuffer *buffer)
 {
     if (!m_surface) {
@@ -244,6 +259,14 @@ void QVideoSurfaceGstDelegate::queuedStop()
     m_setupCondition.wakeAll();
 }
 
+void QVideoSurfaceGstDelegate::queuedFlush()
+{
+    QMutexLocker locker(&m_mutex);
+
+    if (!m_surface.isNull())
+        m_surface->present(QVideoFrame());
+}
+
 void QVideoSurfaceGstDelegate::queuedRender()
 {
     QMutexLocker locker(&m_mutex);
@@ -316,6 +339,8 @@ QVideoSurfaceGstSink *QVideoSurfaceGstSink::createSink(QAbstractVideoSurface *su
 
     sink->delegate = new QVideoSurfaceGstDelegate(surface);
 
+    g_signal_connect(G_OBJECT(sink), "notify::show-preroll-frame", G_CALLBACK(handleShowPrerollChange), sink);
+
     return sink;
 }
 
@@ -420,13 +445,40 @@ void QVideoSurfaceGstSink::finalize(GObject *object)
     G_OBJECT_CLASS(sink_parent_class)->finalize(object);
 }
 
-GstStateChangeReturn QVideoSurfaceGstSink::change_state(
-        GstElement *element, GstStateChange transition)
+void QVideoSurfaceGstSink::handleShowPrerollChange(GObject *o, GParamSpec *p, gpointer d)
 {
-    Q_UNUSED(element);
+    Q_UNUSED(o);
+    Q_UNUSED(p);
+    QVideoSurfaceGstSink *sink = reinterpret_cast<QVideoSurfaceGstSink *>(d);
 
-    return GST_ELEMENT_CLASS(sink_parent_class)->change_state(
-            element, transition);
+    gboolean showPrerollFrame = true; // "show-preroll-frame" property is true by default
+    g_object_get(G_OBJECT(sink), "show-preroll-frame", &showPrerollFrame, NULL);
+
+    if (!showPrerollFrame) {
+        GstState state = GST_STATE_VOID_PENDING;
+        gst_element_get_state(GST_ELEMENT(sink), &state, NULL, GST_CLOCK_TIME_NONE);
+        // show-preroll-frame being set to 'false' while in GST_STATE_PAUSED means
+        // the QMediaPlayer was stopped from the paused state.
+        // We need to flush the current frame.
+        if (state == GST_STATE_PAUSED)
+            sink->delegate->flush();
+    }
+}
+
+GstStateChangeReturn QVideoSurfaceGstSink::change_state(GstElement *element, GstStateChange transition)
+{
+    QVideoSurfaceGstSink *sink = reinterpret_cast<QVideoSurfaceGstSink *>(element);
+
+    gboolean showPrerollFrame = true; // "show-preroll-frame" property is true by default
+    g_object_get(G_OBJECT(element), "show-preroll-frame", &showPrerollFrame, NULL);
+
+    // If show-preroll-frame is 'false' when transitioning from GST_STATE_PLAYING to
+    // GST_STATE_PAUSED, it means the QMediaPlayer was stopped.
+    // We need to flush the current frame.
+    if (transition == GST_STATE_CHANGE_PLAYING_TO_PAUSED && !showPrerollFrame)
+        sink->delegate->flush();
+
+    return GST_ELEMENT_CLASS(sink_parent_class)->change_state(element, transition);
 }
 
 GstCaps *QVideoSurfaceGstSink::get_caps(GstBaseSink *base)

src/multimedia/gsttools_headers/qgstvideorenderersink_p.h

@@ -99,6 +99,8 @@ public:
     void unlock();
     bool proposeAllocation(GstQuery *query);
 
+    void flush();
+
     GstFlowReturn render(GstBuffer *buffer);
 
     bool event(QEvent *event);
@@ -145,6 +147,8 @@ private:
 
     static void finalize(GObject *object);
 
+    static void handleShowPrerollChange(GObject *o, GParamSpec *p, gpointer d);
+
     static GstStateChangeReturn change_state(GstElement *element, GstStateChange transition);
 
     static GstCaps *get_caps(GstBaseSink *sink, GstCaps *filter);

src/multimedia/gsttools_headers/qvideosurfacegstsink_p.h

@@ -96,11 +96,14 @@ public:
     QMutex *poolMutex() { return &m_poolMutex; }
     void clearPoolBuffers();
 
+    void flush();
+
     GstFlowReturn render(GstBuffer *buffer);
 
 private slots:
     void queuedStart();
     void queuedStop();
+    void queuedFlush();
     void queuedRender();
 
     void updateSupportedFormats();
@@ -139,6 +142,8 @@ private:
 
     static void finalize(GObject *object);
 
+    static void handleShowPrerollChange(GObject *o, GParamSpec *p, gpointer d);
+
     static GstStateChangeReturn change_state(GstElement *element, GstStateChange transition);
 
     static GstCaps *get_caps(GstBaseSink *sink);