Share one thread between all AudioOutputControllers instead of creating one per stream.

media/audio/audio_manager.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_MANAGER_H_
+#define MEDIA_AUDIO_AUDIO_MANAGER_H_
+
+#include "base/basictypes.h"
+
+class AudioInputStream;
+class AudioOutputStream;
+class MessageLoop;
+
+// Manages all audio resources. In particular it owns the AudioOutputStream
+// objects. Provides some convenience functions that avoid the need to provide
+// iterators over the existing streams.
+class AudioManager {
+ public:
+  enum Format {
+    AUDIO_PCM_LINEAR = 0,     // PCM is 'raw' amplitude samples.
+    AUDIO_PCM_LOW_LATENCY,    // Linear PCM, low latency requested.
+    AUDIO_MOCK,               // Creates a dummy AudioOutputStream object.
+    AUDIO_LAST_FORMAT         // Only used for validation of format.
+  };
+
+  // Telephone quality sample rate, mostly for speech-only audio.
+  static const uint32 kTelephoneSampleRate = 8000;
+  // CD sampling rate is 44.1 KHz or conveniently 2x2x3x3x5x5x7x7.
+  static const uint32 kAudioCDSampleRate = 44100;
+  // Digital Audio Tape sample rate.
+  static const uint32 kAudioDATSampleRate = 48000;
+
+  // Returns true if the OS reports existence of audio devices. This does not
+  // guarantee that the existing devices support all formats and sample rates.
+  virtual bool HasAudioOutputDevices() = 0;
+
+  // Returns true if the OS reports existence of audio recording devices. This
+  // does not guarantee that the existing devices support all formats and
+  // sample rates.
+  virtual bool HasAudioInputDevices() = 0;
+
+  // Factory for all the supported stream formats. The |channels| can be 1 to 5.
+  // The |sample_rate| is in hertz and can be any value supported by the
+  // platform. For some future formats the |sample_rate| and |bits_per_sample|
+  // can take special values.
+  // Returns NULL if the combination of the parameters is not supported, or if
+  // we have reached some other platform specific limit.
+  //
+  // AUDIO_PCM_LOW_LATENCY can be passed to this method and it has two effects:
+  // 1- Instead of triple buffered the audio will be double buffered.
+  // 2- A low latency driver or alternative audio subsystem will be used when
+  //    available.
+  //
+  // Do not free the returned AudioOutputStream. It is owned by AudioManager.
+  virtual AudioOutputStream* MakeAudioOutputStream(Format format, int channels,
+                                                   int sample_rate,
+                                                   char bits_per_sample) = 0;
+
+  // Factory to create audio recording streams.
+  // |channels| can be 1 or 2.
+  // |sample_rate| is in hertz and can be any value supported by the platform.
+  // |bits_per_sample| can be any value supported by the platform.
+  // |samples_per_packet| is in hertz as well and can be 0 to |sample_rate|,
+  // with 0 suggesting that the implementation use a default value for that
+  // platform.
+  // Returns NULL if the combination of the parameters is not supported, or if
+  // we have reached some other platform specific limit.
+  //
+  // Do not free the returned AudioInputStream. It is owned by AudioManager.
+  // When you are done with it, call |Stop()| and |Close()| to release it.
+  virtual AudioInputStream* MakeAudioInputStream(Format format, int channels,
+                                                 int sample_rate,
+                                                 char bits_per_sample,
+                                                 uint32 samples_per_packet) = 0;
+
+  // Muting continues playback but effectively the volume is set to zero.
+  // Un-muting returns the volume to the previous level.
+  virtual void MuteAll() = 0;
+  virtual void UnMuteAll() = 0;
+
+  // Returns message loop used for audio IO.
+  virtual MessageLoop* GetMessageLoop() = 0;
+
+  // Get AudioManager singleton.
+  // TODO(cpu): Define threading requirements for interacting with AudioManager.
+  static AudioManager* GetAudioManager();
+
+ protected:
+  virtual ~AudioManager() {}
+
+  // Called from GetAudioManager() to initialiaze the instance.
+  virtual void Init() = 0;
+
+ private:
+  static void Destroy(void*);
+
+  // Called by GetAudioManager() to create platform-specific audio manager.
+  static AudioManager* CreateAudioManager();
+};
+
+#endif  // MEDIA_AUDIO_AUDIO_MANAGER_H_