Implement AudioOutputProxy.

media/audio/audio_output_proxy.h

+// Copyright (c) 2010 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef MEDIA_AUDIO_AUDIO_OUTPUT_STREAM_PROXY_H_
+#define MEDIA_AUDIO_AUDIO_OUTPUT_STREAM_PROXY_H_
+
+#include "base/basictypes.h"
+#include "base/task.h"
+#include "media/audio/audio_io.h"
+#include "media/audio/audio_parameters.h"
+
+class AudioOutputDispatcher;
+
+// AudioOutputProxy is an audio otput stream that uses resources more
+// efficiently than a regular audio output stream: it opens audio
+// device only when sound is playing, i.e. between Start() and Stop()
+// (there is still one physical stream per each audio output proxy in
+// playing state).
+//
+// AudioOutputProxy uses AudioOutputDispatcher to open and close
+// physical output streams.
+class AudioOutputProxy : public AudioOutputStream {
+ public:
+  // Caller keeps ownership of |dispatcher|.
+  AudioOutputProxy(AudioOutputDispatcher* dispatcher);
+
+  // AudioOutputStream interface.
+  virtual bool Open();
+  virtual void Start(AudioSourceCallback* callback);
+  virtual void Stop();
+  virtual void SetVolume(double volume);
+  virtual void GetVolume(double* volume);
+  virtual void Close();
+
+ private:
+  // Needs to access destructor.
+  friend class DeleteTask<AudioOutputProxy>;
+
+  enum State {
+    kCreated,
+    kOpened,
+    kPlaying,
+    kClosed,
+    kError,
+  };
+
+  virtual ~AudioOutputProxy();
+
+  scoped_refptr<AudioOutputDispatcher> dispatcher_;
+  State state_;
+
+  // The actual audio stream. Must be set to NULL in any state other
+  // than kPlaying.
+  AudioOutputStream* physical_stream_;
+
+  // Need to save volume here, so that we can restore it in case the stream
+  // is stopped, and then started again.
+  double volume_;
+
+  DISALLOW_COPY_AND_ASSIGN(AudioOutputProxy);
+};
+
+#endif  // MEDIA_AUDIO_AUDIO_OUTPUT_STREAM_PROXY_H_