Add a volume (gain) property to QAudioInput.

Only implemented for PulseAudio so far, but the API does explain that
it's optional.

Change-Id: I4543a1c81d810fe92bb08f1ed13f3a3534a371e4
Reviewed-by: Ling Hu <ling.hu@nokia.com>

src/multimedia/audio/qaudioinput.cpp

@@ -326,6 +326,29 @@ int QAudioInput::notifyInterval() const
     return d->notifyInterval();
 }
 
+/*!
+    Sets the input volume to \a volume.
+
+    If the device does not support adjusting the input
+    volume then \a volume will be ignored and the input
+    volume will remain at 1.0.
+*/
+void QAudioInput::setVolume(qreal volume)
+{
+    d->setVolume(volume);
+}
+
+/*!
+    Returns the input volume (gain).
+
+    If the device does not support adjusting the input volume
+    the returned value will be 1.0.
+*/
+qreal QAudioInput::volume() const
+{
+    return d->volume();
+}
+
 /*!
     Returns the amount of audio data processed since start()
     was called in microseconds.

src/multimedia/audio/qaudioinput.h

@@ -91,6 +91,9 @@ public:
     void setNotifyInterval(int milliSeconds);
     int notifyInterval() const;
 
+    void setVolume(qreal volume);
+    qreal volume() const;
+
     qint64 processedUSecs() const;
     qint64 elapsedUSecs() const;
 

src/multimedia/audio/qaudiosystem.h

@@ -127,6 +127,8 @@ public:
     virtual QAudio::State state() const = 0;
     virtual void setFormat(const QAudioFormat& fmt) = 0;
     virtual QAudioFormat format() const = 0;
+    virtual void setVolume(qreal) {}
+    virtual qreal volume() const { return 1.0; }
 
 Q_SIGNALS:
     void errorChanged(QAudio::Error);