Low-latency AudioInputStream implementation based on WASAPI for Windows.

media/audio/win/audio_low_latency_input_win.h

+// Copyright (c) 2011 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.
+//
+// Implementation of AudioInputStream for Windows using Windows Core Audio
+// WASAPI for low latency capturing.
+//
+// Overview of operation:
+//
+// - An object of WASAPIAudioInputStream is created by the AudioManager
+//   factory.
+// - Next some thread will call Open(), at that point the underlying
+//   Core Audio APIs are utilized to create two WASAPI interfaces called
+//   IAudioClient and IAudioCaptureClient.
+// - Then some thread will call Start(sink).
+//   A thread called "wasapi_capture_thread" is started and this thread listens
+//   on an event signal which is set periodically by the audio engine for
+//   each recorded data packets. As a result, data samples will be provided

[tommi (sloooow) - chröme, 2011/10/14 14:31:04]

each recorded data packet.

[henrika (OOO until Aug 14), 2011/10/17 12:08:24]

Done.

+//   to the registered sink.
+// - At some point, a thread will call Stop(), which stops and joins the
+//   capture thread and at the same time stops audio streaming.
+// - The same thread that called stop will call Close() where we cleanup
+//   and notify the audio manager, which likely will destroy this object.
+//
+// Implementation notes:
+//
+// - The minimum supported client is Windows Vista.
+// - Construction and destruction must take place from the same thread.
+//   It is recommended to call all APIs from the same thread as well.

[tommi (sloooow) - chröme, 2011/10/14 14:31:04]

recommended or required?

I guess as long as the calling thread is an MTA thread, things will work
correctly?

[henrika (OOO until Aug 14), 2011/10/17 12:08:24]

Comment is now more clear.

+// - It is recommended to first acquire the native sample rate of the default
+//   input device and then use the same rate when creating this object. Use
+//   WASAPIAudioInputStream::HardwareSampleRate() to retrieve the sample rate.
+// - Calling Close() also leads to self destruction.

[tommi (sloooow) - chröme, 2011/10/14 14:31:04]

should the initial allocator then not call delete?

[henrika (OOO until Aug 14), 2011/10/17 12:08:24]

The audio manager is the allocator and it deletes this object in Close().

+//
+// Core Audio API details:
+//
+// - CoInitializeEx() is called on the creating thread and on the internal
+//   capture thread. Each thread's concurrency model and apartment is set
+//   to multi-threaded (MTA).

[tommi (sloooow) - chröme, 2011/10/14 14:31:04]

maybe a note that if CoInitializeEx(MTA) fails, then we will check.

[henrika (OOO until Aug 14), 2011/10/17 12:08:24]

Done.

+// - Utilized MMDevice interfaces:
+//     o IMMDeviceEnumerator
+//     o IMMDevice
+// - Utilized WASAPI interfaces:
+//     o IAudioClient
+//     o IAudioCaptureClient
+// - The stream is initialized in shared mode and the processing of the
+//   audio buffer is event driven.
+// - The Multimedia Class Scheduler service (MMCSS) is utilized to boost
+//   the priority of the capture thread.
+//
+#ifndef MEDIA_AUDIO_WIN_AUDIO_LOW_LATENCY_INPUT_WIN_H_
+#define MEDIA_AUDIO_WIN_AUDIO_LOW_LATENCY_INPUT_WIN_H_
+
+#include <MMDeviceAPI.h>
+#include <Audioclient.h>
+
+#include "base/compiler_specific.h"
+#include "base/threading/simple_thread.h"
+#include "base/threading/platform_thread.h"
+#include "base/win/scoped_comptr.h"
+#include "base/win/scoped_handle.h"
+#include "media/audio/audio_io.h"
+#include "media/audio/audio_parameters.h"
+
+class AudioManagerWin;
+
+// Initializes COM in the constructor (MTA), and uninitializes COM in the
+// destructor.
+class ScopedCOMInitializer {

[tommi (sloooow) - chröme, 2011/10/14 14:31:04]

FYI - I have a pending change to support this in ScopedCOMInitializer from base.

[henrika (OOO until Aug 14), 2011/10/17 12:08:24]

Great ;-)

+ public:
+  ScopedCOMInitializer()
+      : hr_(CoInitializeEx(NULL, COINIT_MULTITHREADED)),
+        creating_thread_id_(base::PlatformThread::CurrentId()) {
+    CHECK(SUCCEEDED(hr_));
+  }
+
+  ScopedCOMInitializer::~ScopedCOMInitializer() {
+    DCHECK_EQ(base::PlatformThread::CurrentId(), creating_thread_id_);
+    if (SUCCEEDED(hr_))
+      CoUninitialize();
+  }
+
+ private:
+  base::PlatformThreadId creating_thread_id_;

[tommi (sloooow) - chröme, 2011/10/14 14:31:04]

include only for NDEBUG?

[henrika (OOO until Aug 14), 2011/10/17 12:08:24]

Done.

+  HRESULT hr_;
+  DISALLOW_COPY_AND_ASSIGN(ScopedCOMInitializer);
+};
+
+// A convenience class for COM memory handling.
+template <class T>
+class ScopedComMem {

[tommi (sloooow) - chröme, 2011/10/14 14:31:04]

Andrew - what is the convention on namespaces and platform specific classes like
this?  global namespace?

+ public:
+  ScopedComMem() : ptr_(NULL) {}
+  ~ScopedComMem() {
+    Free();
+  }
+
+  T* operator->() {
+    DCHECK(ptr_ != NULL);
+    return ptr_;
+  }
+
+  T* get() const { return ptr_; }
+
+  T** Receive() {
+    DCHECK(ptr_ == NULL);
+    return &ptr_;
+  }
+
+  void Free() {
+    if (ptr_) {
+      ::CoTaskMemFree(ptr_);
+      ptr_ = NULL;
+    }
+  }
+
+  bool valid() const { return ptr_ != NULL; }
+
+ protected:
+  T* ptr_;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ScopedComMem);
+};
+
+// AudioInputStream implementation using Windows Core Audio APIs.
+class WASAPIAudioInputStream : public AudioInputStream,
+                               public base::DelegateSimpleThread::Delegate {
+ public:
+  // The ctor takes all the usual parameters, plus |manager| which is the
+  // the audio manager who is creating this object.
+  WASAPIAudioInputStream(AudioManagerWin* manager,
+                         const AudioParameters& params,
+                         ERole device_role);
+  // The dtor is typically called by the AudioManager only and it is usually
+  // triggered by calling AudioInputStream::Close().
+  virtual ~WASAPIAudioInputStream();
+
+  // Implementation of AudioInputStream.
+  virtual bool Open() OVERRIDE;
+  virtual void Start(AudioInputCallback* callback) OVERRIDE;
+  virtual void Stop() OVERRIDE;
+  virtual void Close() OVERRIDE;
+
+  // Retrieve the stream format that the audio engine uses for its internal
+  // processing/mixing of shared-mode streams.
+  static double HardwareSampleRate(ERole device_role);
+
+  bool started() const { return started_; }
+
+ private:
+  // DelegateSimpleThread::Delegate implementation.
+  virtual void Run() OVERRIDE;
+
+  // Issues the OnError() callback to the |sink_|.
+  void HandleError(HRESULT err);
+
+  // The Open() method is divided into these sub methods.
+  HRESULT SetCaptureDevice(ERole device_role);
+  HRESULT ActivateCaptureDevice();
+  HRESULT GetAudioEngineStreamFormat();
+  bool DesiredFormatIsSupported();
+  HRESULT InitializeAudioEngine();
+
+  // Initializes the COM library for use by the calling thread and set the
+  // thread's concurrency model to multi-threaded.
+  ScopedCOMInitializer com_init_;
+
+  // Our creator, the audio manager needs to be notified when we close.
+  AudioManagerWin* manager_;
+
+  // Capturing is driven by this thread (which has no message loop).
+  // All OnData() callbacks will be called from this thread.
+  base::DelegateSimpleThread* capture_thread_;
+
+  // Contains the desired audio format which is set up at construction.
+  WAVEFORMATEX format_;
+
+  // Copy of the audio format which we know the audio engine supports.
+  // It is recommended to ensure that the sample rate in |format_| is identical
+  // to the sample rate in |audio_engine_mix_format_|.
+  ScopedComMem<WAVEFORMATEX> audio_engine_mix_format_;
+
+  bool opened_;
+  bool started_;
+
+  // Size in bytes of each audio frame (4 bytes for 16-bit stereo PCM)
+  size_t frame_size_;
+
+  // Size in audio frames of each audio packet where an audio packet
+  // is defined as the block of data which the user received in each
+  // OnData() callback.
+  size_t packet_size_frames_;
+
+  // Size in bytes of each audio packet.
+  size_t packet_size_bytes_;
+
+  // Size in milliseconds of each audio packet.

[Niklas Enbom, 2011/10/14 14:46:51]

This value seems to be calculated but never used?

[henrika (OOO until Aug 14), 2011/10/17 12:08:24]

Ooops. Removed.

+  float packet_size_ms_;
+
+  // Length of the audio endpoint buffer.
+  size_t endpoint_buffer_size_frames_;
+
+  // Defines the role that the system has assigned to an audio endpoint device.
+  ERole device_role_;
+
+  // Conversion factor used in delay-estimation calculations.
+  // Converts a raw performance counter value to 100-nanosecond unit.
+  double perf_count_to_100ns_units_;
+
+  // Conversion factor used in delay-estimation calculations.
+  // Converts from milliseconds to audio frames.
+  double ms_to_frame_count_;
+
+  // Pointer to the object that will receive the recorded audio samples.
+  AudioInputCallback* sink_;
+
+  // An IMMDevice interface which represents an audio endpoint device.
+  base::win::ScopedComPtr<IMMDevice> endpoint_device_;
+
+  // An IAudioClient interface which enables a client to create and initialize
+  // an audio stream between an audio application and the audio engine.
+  base::win::ScopedComPtr<IAudioClient> audio_client_;
+
+  // The IAudioCaptureClient interface enables a client to read input data
+  // from a capture endpoint buffer.
+  base::win::ScopedComPtr<IAudioCaptureClient> audio_capture_client_;
+
+  // The audio engine will signal this event each time a buffer has been
+  // recorded.
+  base::win::ScopedHandle audio_samples_ready_event_;
+
+  // This event will be signaled when capturing shall stop.
+  base::win::ScopedHandle stop_capture_event_;
+
+  DISALLOW_COPY_AND_ASSIGN(WASAPIAudioInputStream);
+};
+
+#endif  // MEDIA_AUDIO_WIN_AUDIO_LOW_LATENCY_INPUT_WIN_H_