Changes to QMediaPlayer GStreamer backend to allow setPosition before pause

Do not display prerolled frames in stopped state.
Instead store prerolled frame and display it only after switching to
pause or playback state.
Added new unit test with a sample video file to check this functionality.

Change-Id: I3fd159a199b65ca10fdf9843af5675c5ae9dad05
Reviewed-by: Michael Goddard <michael.goddard@nokia.com>

src/gsttools/qvideosurfacegstsink.cpp

@@ -66,6 +66,7 @@ QVideoSurfaceGstDelegate::QVideoSurfaceGstDelegate(
     : m_surface(surface)
     , m_pool(0)
     , m_renderReturn(GST_FLOW_ERROR)
+    , m_lastPrerolledBuffer(0)
     , m_bytesPerLine(0)
     , m_startCanceled(false)
 {
@@ -87,6 +88,7 @@ QVideoSurfaceGstDelegate::QVideoSurfaceGstDelegate(
 QVideoSurfaceGstDelegate::~QVideoSurfaceGstDelegate()
 {
     qDeleteAll(m_pools);
+    setLastPrerolledBuffer(0);
 }
 
 QList<QVideoFrame::PixelFormat> QVideoSurfaceGstDelegate::supportedPixelFormats(QAbstractVideoBuffer::HandleType handleType) const
@@ -222,6 +224,23 @@ GstFlowReturn QVideoSurfaceGstDelegate::render(GstBuffer *buffer)
     return m_renderReturn;
 }
 
+void QVideoSurfaceGstDelegate::setLastPrerolledBuffer(GstBuffer *prerolledBuffer)
+{
+    // discard previously stored buffer
+    if (m_lastPrerolledBuffer) {
+        gst_buffer_unref(m_lastPrerolledBuffer);
+        m_lastPrerolledBuffer = 0;
+    }
+
+    if (!prerolledBuffer)
+        return;
+
+    // store a reference to the buffer
+    Q_ASSERT(!m_lastPrerolledBuffer);
+    m_lastPrerolledBuffer = prerolledBuffer;
+    gst_buffer_ref(m_lastPrerolledBuffer);
+}
+
 void QVideoSurfaceGstDelegate::queuedStart()
 {
     if (!m_startCanceled) {
@@ -393,6 +412,8 @@ 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;
 }
 
@@ -435,7 +456,7 @@ void QVideoSurfaceGstSink::class_init(gpointer g_class, gpointer class_data)
     base_sink_class->start = QVideoSurfaceGstSink::start;
     base_sink_class->stop = QVideoSurfaceGstSink::stop;
     // base_sink_class->unlock = QVideoSurfaceGstSink::unlock; // Not implemented.
-    // base_sink_class->event = QVideoSurfaceGstSink::event; // Not implemented.
+    base_sink_class->event = QVideoSurfaceGstSink::event;
     base_sink_class->preroll = QVideoSurfaceGstSink::preroll;
     base_sink_class->render = QVideoSurfaceGstSink::render;
 
@@ -664,6 +685,26 @@ QVideoSurfaceFormat QVideoSurfaceGstSink::formatForCaps(GstCaps *caps, int *byte
     return QVideoSurfaceFormat();
 }
 
+void QVideoSurfaceGstSink::handleShowPrerollChange(GObject *o, GParamSpec *p, gpointer d)
+{
+    Q_UNUSED(o);
+    Q_UNUSED(p);
+    QVideoSurfaceGstSink *sink = reinterpret_cast<QVideoSurfaceGstSink *>(d);
+
+    gboolean value = true; // "show-preroll-frame" property is true by default
+    g_object_get(G_OBJECT(sink), "show-preroll-frame", &value, NULL);
+
+    GstBuffer *buffer = sink->delegate->lastPrerolledBuffer();
+    // Render the stored prerolled buffer if requested.
+    // e.g. player is in stopped mode, then seek operation is requested,
+    // surface now stores a prerolled frame, but doesn't display it until
+    // "show-preroll-frame" property is set to "true"
+    // when switching to pause or playing state.
+    if (value && buffer) {
+        sink->delegate->render(buffer);
+        sink->delegate->setLastPrerolledBuffer(0);
+    }
+}
 
 GstFlowReturn QVideoSurfaceGstSink::buffer_alloc(
         GstBaseSink *base, guint64 offset, guint size, GstCaps *caps, GstBuffer **buffer)
@@ -781,8 +822,11 @@ gboolean QVideoSurfaceGstSink::unlock(GstBaseSink *base)
 
 gboolean QVideoSurfaceGstSink::event(GstBaseSink *base, GstEvent *event)
 {
-    Q_UNUSED(base);
-    Q_UNUSED(event);
+    // discard prerolled frame
+    if (event->type == GST_EVENT_FLUSH_START) {
+        VO_SINK(base);
+        sink->delegate->setLastPrerolledBuffer(0);
+    }
 
     return TRUE;
 }
@@ -790,12 +834,23 @@ gboolean QVideoSurfaceGstSink::event(GstBaseSink *base, GstEvent *event)
 GstFlowReturn QVideoSurfaceGstSink::preroll(GstBaseSink *base, GstBuffer *buffer)
 {
     VO_SINK(base);
-    return sink->delegate->render(buffer);
+
+    gboolean value = true; // "show-preroll-frame" property is true by default
+    g_object_get(G_OBJECT(base), "show-preroll-frame", &value, NULL);
+    if (value) {
+        sink->delegate->setLastPrerolledBuffer(0); // discard prerolled buffer
+        return sink->delegate->render(buffer); // display frame
+    }
+
+    // otherwise keep a reference to the buffer to display it later
+    sink->delegate->setLastPrerolledBuffer(buffer);
+    return GST_FLOW_OK;
 }
 
 GstFlowReturn QVideoSurfaceGstSink::render(GstBaseSink *base, GstBuffer *buffer)
 {
     VO_SINK(base);
+    sink->delegate->setLastPrerolledBuffer(0); // discard prerolled buffer
     return sink->delegate->render(buffer);
 }