Gst player backend: don't show the first frame when resuming playback.

It's necessary to temporarily disable show-preroll-frame of video sink,
load pipeline to paused state, seek to requested position,
and after seeking is finished (position updated) playback is started
with show-preroll-frame restored.

Task-number: MOBILITY-3030
Reviewed-by: Jonas Rabbe
Change-Id: Ide1e6d909dd53f670229c293bc6be496a54e8626
(cherry picked from commit 625cce87e28fc7b5ec8785824affb3129fd3607b)
Reviewed-on: http://codereview.qt-project.org/5500
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Jonas Rabbe <jonas.rabbe@nokia.com>

src/plugins/gstreamer/mediaplayer/qgstreamerplayercontrol.cpp

@@ -79,7 +79,7 @@ QGstreamerPlayerControl::QGstreamerPlayerControl(QGstreamerPlayerSession *sessio
     m_resources = new PlayerResourcePolicy(this);
 
     connect(m_session, SIGNAL(positionChanged(qint64)),
-            this, SIGNAL(positionChanged(qint64)));
+            this, SLOT(updatePosition(qint64)));
     connect(m_session, SIGNAL(durationChanged(qint64)),
             this, SIGNAL(durationChanged(qint64)));
     connect(m_session, SIGNAL(mutedStateChanged(bool)),
@@ -195,9 +195,10 @@ void QGstreamerPlayerControl::setPosition(qint64 pos)
 
     if (m_session->isSeekable() && m_session->seek(pos)) {
         m_seekToStartPending = false;
-        m_pendingSeekPosition = -1;
     } else {
         m_pendingSeekPosition = pos;
+        //don't display the first video frame since it's not what user requested.
+        m_session->showPrerollFrames(false);
     }
 
     popAndNotifyState();
@@ -256,7 +257,11 @@ void QGstreamerPlayerControl::playOrPause(QMediaPlayer::State newState)
 
         bool ok = false;
 
-        if (newState == QMediaPlayer::PlayingState)
+        //To prevent displaying the first video frame when playback is resumed
+        //the pipeline is paused instead of playing, seeked to requested position,
+        //and after seeking is finished (position updated) playback is restarted
+        //with show-preroll-frame enabled.
+        if (newState == QMediaPlayer::PlayingState && m_pendingSeekPosition == -1)
             ok = m_session->play();
         else
             ok = m_session->pause();
@@ -335,6 +340,7 @@ void QGstreamerPlayerControl::setMedia(const QMediaContent &content, QIODevice *
     m_state = QMediaPlayer::StoppedState;
     QMediaContent oldMedia = m_currentResource;
     m_pendingSeekPosition = -1;
+    m_session->showPrerollFrames(true);
 
     if (!content.isNull() || stream) {
         if (!m_resources->isRequested() && !m_resources->isGranted())
@@ -700,6 +706,8 @@ void QGstreamerPlayerControl::handleResourcesLost()
     qint64 pos = m_session->position();
     m_session->stop();
     m_pendingSeekPosition = pos;
+    //don't blink the first video frame after playback is restored
+    m_session->showPrerollFrames(false);
 
     if (oldState != QMediaPlayer::StoppedState )
         m_state = QMediaPlayer::PausedState;
@@ -746,3 +754,22 @@ void QGstreamerPlayerControl::popAndNotifyState()
         }
     }
 }
+
+void QGstreamerPlayerControl::updatePosition(qint64 pos)
+{
+#ifdef DEBUG_PLAYBIN
+    qDebug() << Q_FUNC_INFO << pos/1000.0 << "pending:" << m_pendingSeekPosition/1000.0;
+#endif
+
+    if (m_pendingSeekPosition != -1) {
+        //seek request is complete, it's safe to resume playback
+        //with prerolled frame displayed
+        m_pendingSeekPosition = -1;
+        m_session->showPrerollFrames(true);
+        if (m_state == QMediaPlayer::PlayingState) {
+            m_session->play();
+        }
+    }
+
+    emit positionChanged(pos);
+}

src/plugins/gstreamer/mediaplayer/qgstreamerplayercontrol.h

@@ -118,6 +118,7 @@ private Q_SLOTS:
     void processEOS();
     void setBufferProgress(int progress);
     void applyPendingSeek(bool isSeekable);
+    void updatePosition(qint64 pos);
 
     void handleInvalidMedia();
 

src/plugins/gstreamer/mediaplayer/qgstreamerplayersession.cpp

@@ -103,6 +103,7 @@ QGstreamerPlayerSession::QGstreamerPlayerSession(QObject *parent)
      m_lastPosition(0),
      m_duration(-1),
      m_durationQueries(0),
+     m_displayPrerolledFrame(true),
      m_sourceType(UnknownSrc),
      m_everPlayed(false),
      m_isLiveSource(false)
@@ -536,6 +537,11 @@ void QGstreamerPlayerSession::setVideoRenderer(QObject *videoOutput)
             linked = gst_element_link_many(m_videoIdentity, m_colorSpace, m_videoSink, NULL);
         }
 
+        if (g_object_class_find_property(G_OBJECT_GET_CLASS(m_videoSink), "show-preroll-frame") != 0) {
+            gboolean value = m_displayPrerolledFrame;
+            g_object_set(G_OBJECT(m_videoSink), "show-preroll-frame", value, NULL);
+        }
+
         switch (m_pendingState) {
         case QMediaPlayer::PausedState:
             gst_element_set_state(m_playbin, GST_STATE_PAUSED);
@@ -1596,3 +1602,17 @@ void QGstreamerPlayerSession::processInvalidMedia(QMediaPlayer::Error errorCode,
     stop();
     emit error(int(errorCode), errorString);
 }
+
+void QGstreamerPlayerSession::showPrerollFrames(bool enabled)
+{
+#ifdef DEBUG_PLAYBIN
+    qDebug() << Q_FUNC_INFO << enabled;
+#endif
+    if (enabled != m_displayPrerolledFrame && m_videoSink &&
+            g_object_class_find_property(G_OBJECT_GET_CLASS(m_videoSink), "show-preroll-frame") != 0) {
+
+        gboolean value = enabled;
+        g_object_set(G_OBJECT(m_videoSink), "show-preroll-frame", value, NULL);
+        m_displayPrerolledFrame = enabled;
+    }
+}

src/plugins/gstreamer/mediaplayer/qgstreamerplayersession.h

@@ -131,6 +131,8 @@ public slots:
     void setVolume(int volume);
     void setMuted(bool muted);
 
+    void showPrerollFrames(bool enabled);
+
 signals:
     void durationChanged(qint64 duration);
     void positionChanged(qint64 position);
@@ -209,6 +211,8 @@ private:
     qint64 m_duration;
     int m_durationQueries;
 
+    bool m_displayPrerolledFrame;
+
     enum SourceType
     {
         UnknownSrc,