AudioCore: Skeleton Implementation

This commit:
* Adds a new subproject, audio_core.
* Defines structures that exist in DSP shared memory.
* Hooks up various other parts of the emulator into audio core.

This sets the foundation for a later HLE DSP implementation.

src/audio_core/sink.h

@@ -0,0 +1,34 @@
+// Copyright 2016 Citra Emulator Project
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <vector>
+
+#include "common/common_types.h"
+
+namespace AudioCore {
+
+/**
+ * This class is an interface for an audio sink. An audio sink accepts samples in stereo signed PCM16 format to be output.
+ * Sinks *do not* handle resampling and expect the correct sample rate. They are dumb outputs.
+ */
+class Sink {
+public:
+    virtual ~Sink() = default;
+
+    /// The native rate of this sink. The sink expects to be fed samples that respect this. (Units: samples/sec)
+    virtual unsigned GetNativeSampleRate() const = 0;
+
+    /**
+     * Feed stereo samples to sink.
+     * @param samples Samples in interleaved stereo PCM16 format. Size of vector must be multiple of two.
+     */
+    virtual void EnqueueSamples(const std::vector<s16>& samples) = 0;
+
+    /// Samples enqueued that have not been played yet.
+    virtual std::size_t SamplesInQueue() const = 0;
+};
+
+} // namespace