refs #372 Add audio mixer interface and vatlib implementation

This class is an audio router. In order to route audio connect a
producer to an input port and a consumer to an output port. The
connection is later established by making the mixer connection
between an input and an output port.

src/blackcore/audio_mixer.h

@@ -0,0 +1,61 @@
+/* Copyright (C) 2014
+ * swift project community / contributors
+ *
+ * This file is part of swift project. It is subject to the license terms in the LICENSE file found in the top-level
+ * directory of this distribution and at http://www.swift-project.org/license.html. No part of swift project,
+ * including this file, may be copied, modified, propagated, or distributed except according to the terms
+ * contained in the LICENSE file.
+ */
+
+#ifndef BLACKCORE_AUDIOMIXER_H
+#define BLACKCORE_AUDIOMIXER_H
+
+#include <QObject>
+
+namespace BlackCore
+{
+    //! Interface to an audio mixer
+    class IAudioMixer : public QObject
+    {
+        Q_OBJECT
+
+    public:
+
+        //! Audio mixer input ports
+        enum InputPort
+        {
+            InputMicrophone,
+            InputVoiceChannel1,
+            InputVoiceChannel2,
+        };
+
+        //! Audio mixer output ports
+        enum OutputPort
+        {
+            OutputOutputDevice1,
+            OutputVoiceChannel1,
+            OutputVoiceChannel2,
+        };
+
+        /*!
+         * \brief Default constructor with parent
+         * \param parent
+         */
+        IAudioMixer(QObject *parent = nullptr);
+
+        //! Virtual destructor.
+        virtual ~IAudioMixer() {}
+
+        //! Connect mixer input to a mixer output. This causes audio to be routed from the input to output
+        virtual void makeMixerConnection(InputPort inputPort, OutputPort outputPort) = 0;
+
+        //! Remove the mixer connection from input to output
+        virtual void removeMixerConnection(InputPort inputPort, OutputPort outputPort) = 0;
+
+        //! Returns true if input port and output port are connected
+        virtual bool hasMixerConnection(InputPort inputPort, OutputPort outputPort) = 0;
+    };
+
+} // namespace BlackCore
+
+#endif // guard