GStreamer: each QMediaPlayer now has its own volume by default.

We were using the volume property of GStreamer's playbin element to set
the volume. This could behave differently depending on the system
configuration; it could affect the system volume or the media player
own audio stream.
We now use a 'volume' element to do software attenuation on the audio
data sent to the audio sink, it allows each QMediaPlayer to always have
its own volume.
To preserve the previous behavior, developers can set the
QT_GSTREAMER_USE_PLAYBIN_VOLUME environment variable to true.

[ChangeLog][QtMultimedia][GStreamer] QMediaPlayer::setVolume() doesn't
change the system volume anymore (it could be the case before depending
on the system configuration). Set the QT_GSTREAMER_USE_PLAYBIN_VOLUME
environment variable to true to restore that behavior.

Task-number: QTBUG-30317
Task-number: QTBUG-36511

Change-Id: Ia0249962a74ac21fb110fcb634c08706f8d5767a
Reviewed-by: Wouter Huysentruit <wouter_huysentruit@hotmail.com>
Reviewed-by: Christian Stromme <christian.stromme@digia.com>

2 files changed, 49 insertions, 13 deletions

diff --git a/src/plugins/gstreamer/mediaplayer/qgstreamerplayersession.cpp b/src/plugins/gstreamer/mediaplayer/qgstreamerplayersession.cpp
index f4ac59420..f7522a5f7 100644
--- a/src/plugins/gstreamer/mediaplayer/qgstreamerplayersession.cpp
+++ b/src/plugins/gstreamer/mediaplayer/qgstreamerplayersession.cpp
@@ -67,6 +67,20 @@
 
 QT_BEGIN_NAMESPACE
 
+static bool usePlaybinVolume()
+{
+    static enum { Yes, No, Unknown } status = Unknown;
+    if (status == Unknown) {
+        QByteArray v = qgetenv("QT_GSTREAMER_USE_PLAYBIN_VOLUME");
+        bool value = !v.isEmpty() && v != "0" && v != "false";
+        if (value)
+            status = Yes;
+        else
+            status = No;
+    }
+    return status == Yes;
+}
+
 typedef enum {
     GST_PLAY_FLAG_VIDEO         = 0x00000001,
     GST_PLAY_FLAG_AUDIO         = 0x00000002,
@@ -104,6 +118,7 @@ QGstreamerPlayerSession::QGstreamerPlayerSession(QObject *parent)
      m_pendingVideoSink(0),
      m_nullVideoSink(0),
      m_audioSink(0),
+     m_volumeElement(0),
      m_bus(0),
      m_videoOutput(0),
      m_renderer(0),
@@ -151,8 +166,28 @@ QGstreamerPlayerSession::QGstreamerPlayerSession(QObject *parent)
 #endif
         g_object_set(G_OBJECT(m_playbin), "flags", flags, NULL);
 
-        m_audioSink = gst_element_factory_make("autoaudiosink", "audiosink");
-        if (m_audioSink) {
+        GstElement *audioSink = gst_element_factory_make("autoaudiosink", "audiosink");
+        if (audioSink) {
+            if (usePlaybinVolume()) {
+                m_audioSink = audioSink;
+                m_volumeElement = m_playbin;
+            } else {
+                m_volumeElement = gst_element_factory_make("volume", "volumeelement");
+                if (m_volumeElement) {
+                    m_audioSink = gst_bin_new("audio-output-bin");
+
+                    gst_bin_add_many(GST_BIN(m_audioSink), m_volumeElement, audioSink, NULL);
+                    gst_element_link(m_volumeElement, audioSink);
+
+                    GstPad *pad = gst_element_get_static_pad(m_volumeElement, "sink");
+                    gst_element_add_pad(GST_ELEMENT(m_audioSink), gst_ghost_pad_new("sink", pad));
+                    gst_object_unref(GST_OBJECT(pad));
+                } else {
+                    m_audioSink = audioSink;
+                    m_volumeElement = m_playbin;
+                }
+            }
+
             g_object_set(G_OBJECT(m_playbin), "audio-sink", m_audioSink, NULL);
             addAudioBufferProbe();
         }
@@ -193,12 +228,12 @@ QGstreamerPlayerSession::QGstreamerPlayerSession(QObject *parent)
         g_signal_connect(G_OBJECT(m_playbin), "notify::source", G_CALLBACK(playbinNotifySource), this);
         g_signal_connect(G_OBJECT(m_playbin), "element-added",  G_CALLBACK(handleElementAdded), this);
 
-        // Init volume and mute state
-        g_object_set(G_OBJECT(m_playbin), "volume", 1.0, NULL);
-        g_object_set(G_OBJECT(m_playbin), "mute", FALSE, NULL);
-
-        g_signal_connect(G_OBJECT(m_playbin), "notify::volume", G_CALLBACK(handleVolumeChange), this);
-        g_signal_connect(G_OBJECT(m_playbin), "notify::mute", G_CALLBACK(handleMutedChange), this);
+        if (usePlaybinVolume()) {
+            updateVolume();
+            updateMuted();
+            g_signal_connect(G_OBJECT(m_playbin), "notify::volume", G_CALLBACK(handleVolumeChange), this);
+            g_signal_connect(G_OBJECT(m_playbin), "notify::mute", G_CALLBACK(handleMutedChange), this);
+        }
 
         g_signal_connect(G_OBJECT(m_playbin), "video-changed", G_CALLBACK(handleStreamsChange), this);
         g_signal_connect(G_OBJECT(m_playbin), "audio-changed", G_CALLBACK(handleStreamsChange), this);
@@ -912,10 +947,8 @@ void QGstreamerPlayerSession::setVolume(int volume)
     if (m_volume != volume) {
         m_volume = volume;
 
-        if (m_playbin) {
-            //playbin2 allows to set volume and muted independently,
-            g_object_set(G_OBJECT(m_playbin), "volume", m_volume/100.0, NULL);
-        }
+        if (m_volumeElement)
+            g_object_set(G_OBJECT(m_volumeElement), "volume", m_volume / 100.0, NULL);
 
         emit volumeChanged(m_volume);
     }
@@ -929,7 +962,9 @@ void QGstreamerPlayerSession::setMuted(bool muted)
     if (m_muted != muted) {
         m_muted = muted;
 
-        g_object_set(G_OBJECT(m_playbin), "mute", m_muted ? TRUE : FALSE, NULL);
+        if (m_volumeElement)
+            g_object_set(G_OBJECT(m_volumeElement), "mute", m_muted ? TRUE : FALSE, NULL);
+
         emit mutedStateChanged(m_muted);
     }
 }
diff --git a/src/plugins/gstreamer/mediaplayer/qgstreamerplayersession.h b/src/plugins/gstreamer/mediaplayer/qgstreamerplayersession.h
index 94a84e5dd..23e70315b 100644
--- a/src/plugins/gstreamer/mediaplayer/qgstreamerplayersession.h
+++ b/src/plugins/gstreamer/mediaplayer/qgstreamerplayersession.h
@@ -211,6 +211,7 @@ private:
     GstElement* m_nullVideoSink;
 
     GstElement* m_audioSink;
+    GstElement* m_volumeElement;
 
     GstBus* m_bus;
     QObject *m_videoOutput;