Add Mac OS X synchronized audio I/O back-end

media/audio/mac/audio_synchronized_mac.h

+// Copyright (c) 2012 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.
+//
+// AudioSynchronizedStream allows arbitrary combinations of input and output
+// devices running off different clocks and using different drivers, with
+// potentially differing sample-rates.  It implements AudioOutputStream
+// and shuttles its synchronized I/O data using AudioSourceCallback.
+//
+// It is required to first acquire the native sample rate of the selected
+// output device and then use the same rate when creating this object.
+//
+
+// ............................................................................
+// Theory of Operation:
+//                                       .
+//      INPUT THREAD                     .             OUTPUT THREAD
+//   +-----------------+     +------+    .
+//   | Input AudioUnit | --> |      |    .
+//   +-----------------+     |      |    .
+//                           | FIFO |    .
+//                           |      |        +-----------+
+//                           |      | -----> | Varispeed |
+//                           |      |        +-----------+
+//                           +------+    .         |
+//                                       .         |              +-----------+
+//                                       .    OnMoreIOData() -->  | Output AU |
+//                                       .                        +-----------+
+//
+// The input AudioUnit's InputProc is called on one thread which feeds the
+// FIFO.  The output AudioUnit's OutputProc is called on a second thread
+// which pulls on the varispeed to get the current input data.  The varispeed
+// handles mismatches between input and output sample-rate and also clock drift

[no longer working on chromium, 2012/09/12 09:11:56]

So the FIFO is thread safe?

[Chris Rogers, 2012/09/13 01:03:05]

Good catch!  The AudioFifo is currently *not* thread-safe because of the
|frames_| variable.  However, we can make it thread-safe by getting rid of this
variable and calculating it based off read_pos_ and write_pos_ (or similar
techniques) --- in other words turn it into a classic lock-free circular buffer.

In the meantime, as a very temporary stop-gap fix, I've added |fifo_lock_| and
try-lock around the use of the FIFO.  This isn't good, since it can cause
glitches, but at least will not be dangerous in terms of crashes.

+// between the input and output drivers.  The varispeed consumes its data from
+// the FIFO and adjusts its rate dynamically according to the amount
+// of data buffered in the FIFO.  If the FIFO starts getting too much data
+// buffered then the varispeed will speed up slightly to compensate
+// and similarly if the FIFO doesn't have enough data buffered then the
+// varispeed will slow down slightly.

[scherkus (not reviewing), 2012/09/12 14:05:29]

can you move comment to be next to class?

[Chris Rogers, 2012/09/13 01:03:05]

Done.

+//
+// Finally, once the input data is available then OnMoreIOData() is called
+// which is given this input, and renders the output which is finally sent
+// to the Output AudioUnit.
+
+#ifndef MEDIA_AUDIO_MAC_AUDIO_SYNCHRONIZED_MAC_H_
+#define MEDIA_AUDIO_MAC_AUDIO_SYNCHRONIZED_MAC_H_
+
+#include <AudioToolbox/AudioToolbox.h>
+#include <AudioUnit/AudioUnit.h>
+#include <CoreAudio/CoreAudio.h>
+
+#define CHROME 0
+
+#if CHROME

[no longer working on chromium, 2012/09/12 09:11:56]

what is this?

[Chris Rogers, 2012/09/13 01:03:05]

Sorry, this is temporary which I need for testing for the next day or so, so I
don't expect an LGTM until it's removed :)

+  #include "base/compiler_specific.h"
+  #include "media/audio/audio_io.h"
+  #include "media/audio/audio_parameters.h"
+  #include "media/base/audio_fifo.h"
+#else
+  #include "audio_parameters.h"
+  #include "AudioFIFO.h"
+#endif
+
+namespace media {
+
+class AudioManagerMac;
+
+class AudioSynchronizedStream : public AudioOutputStream {
+ public:
+  // The ctor takes all the usual parameters, plus |manager| which is the
+  // the audio manager who is creating this object.
+  AudioSynchronizedStream(AudioManagerMac* manager,
+                          const AudioParameters& params,
+                          AudioDeviceID input_id,
+                          AudioDeviceID output_id);
+
+  virtual ~AudioSynchronizedStream();
+
+  // Implementation of AudioOutputStream.
+  virtual bool Open() OVERRIDE;
+  virtual void Close() OVERRIDE;
+  virtual void Start(AudioSourceCallback* callback) OVERRIDE;
+  virtual void Stop() OVERRIDE;
+
+  // TODO(crogers):
+  // implement - or remove SetVolume()/GetVolume() from AudioOutputStream.

[scherkus (not reviewing), 2012/09/12 14:05:29]

agreed :)

+  virtual void SetVolume(double volume) OVERRIDE {}

[scherkus (not reviewing), 2012/09/12 14:05:29]

de-inline virtual methods

[Chris Rogers, 2012/09/13 01:03:05]

Done.

+  virtual void GetVolume(double* volume) OVERRIDE {}
+
+  OSStatus SetInputDeviceAsCurrent(AudioDeviceID input_id);
+  OSStatus SetOutputDeviceAsCurrent(AudioDeviceID output_id);
+  AudioDeviceID GetInputDeviceID() { return input_info_.id_;  }
+  AudioDeviceID GetOutputDeviceID() { return output_info_.id_; }
+
+  bool IsRunning();
+
+ private:
+  // Initialization.
+  OSStatus CreateAudioUnits();
+  OSStatus SetupInput(AudioDeviceID input_id);
+  OSStatus EnableIO();
+  OSStatus SetupOutput(AudioDeviceID output_id);
+  OSStatus SetupCallbacks();
+  OSStatus SetupStreamFormats();
+
+  void ComputeThruOffset();
+
+  // AudioUnit callbacks.
+  static OSStatus InputProc(void* user_data,
+                            AudioUnitRenderActionFlags* io_action_flags,
+                            const AudioTimeStamp* time_stamp,
+                            UInt32 bus_number,
+                            UInt32 number_of_frames,
+                            AudioBufferList* io_data);
+
+  static OSStatus VarispeedProc(void* user_data,
+                                AudioUnitRenderActionFlags* io_action_flags,
+                                const AudioTimeStamp* time_stamp,
+                                UInt32 bus_number,
+                                UInt32 number_of_frames,
+                                AudioBufferList* io_data);
+
+  static OSStatus OutputProc(void* user_data,
+                             AudioUnitRenderActionFlags* io_action_flags,
+                             const AudioTimeStamp* time_stamp,
+                             UInt32 bus_number,
+                             UInt32 number_of_frames,
+                             AudioBufferList*  io_data);
+
+  // Our creator.
+  AudioManagerMac* manager_;
+
+  // Pointer to the object that will provide the audio samples.
+  AudioSourceCallback* source_;
+
+  // Values used in Open().
+  AudioDeviceID input_id_;
+  AudioDeviceID output_id_;
+
+  AudioBufferList* input_buffer_;
+
+  struct AudioDeviceInfo {

[no longer working on chromium, 2012/09/12 09:11:56]

it contains member functions in this struct, we should use class instead.

[Chris Rogers, 2012/09/13 01:03:05]

Done.

+    AudioDeviceInfo() : id_(kAudioDeviceUnknown) {}
+    void Initialize(AudioDeviceID inID, bool isInput);
+    bool IsInitialized() const { return id_ != kAudioDeviceUnknown; }
+
+    AudioDeviceID id_;
+    bool is_input_;
+    UInt32 buffer_size_frames_;

[no longer working on chromium, 2012/09/12 09:11:56]

initialize these values in the constructor.

[Chris Rogers, 2012/09/13 01:03:05]

Done.

+  };
+
+  AudioDeviceInfo input_info_;
+  AudioDeviceInfo output_info_;
+
+  // Used for input to output buffering.
+  AudioFifo fifo_;
+  bool is_fifo_initialized_;
+  double fifo_rate_compensation_;
+  double output_sample_rate_;
+
+  // AudioUnits

[scherkus (not reviewing), 2012/09/12 14:05:29]

period

[Chris Rogers, 2012/09/13 01:03:05]

Done.

+  AudioUnit input_unit_;
+  AudioUnit varispeed_unit_;
+  AudioUnit output_unit_;
+
+  // Initial latency estimation.
+  Float64 first_input_time_;

[scherkus (not reviewing), 2012/09/12 14:05:29]

are we required to use these types vs. double?

[Chris Rogers, 2012/09/13 01:03:05]

You're right - not in this case -- switched to double

+  Float64 first_output_time_;
+  Float64 in_to_out_sample_offset_;
+
+  bool is_running_;
+  UInt32 hardware_frame_size_;
+};

[scherkus (not reviewing), 2012/09/12 14:05:29]

DISALLOW etc

[Chris Rogers, 2012/09/13 01:03:05]

Done.

+
+}  // namespace media
+
+#endif  // MEDIA_AUDIO_MAC_AUDIO_SYNCHRONIZED_MAC_H_