Adding input and output delay estimation for mac.

media/audio/mac/audio_low_latency_input_mac.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 Mac OS X using the special AUHAL
 // input Audio Unit present in OS 10.4 and later.
 // The AUHAL input Audio Unit is for low-latency audio I/O.
 //
 // Overview of operation:
 //
 // - An object of AUAudioInputStream is created by the AudioManager
 //   factory: audio_man->MakeAudioInputStream().
 // - Next some thread will call Open(), at that point the underlying
 //   AUHAL output Audio Unit is created and configured.
 // - Then some thread will call Start(sink).
 //   Then the Audio Unit is started which creates its own thread which
 //   periodically will provide the sink with more data as buffers are being
 //   produced/recorded.
 // - At some point some thread will call Stop(), which we handle by directly
 //   stopping the AUHAL output Audio Unit.
 // - 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:
 //
 // - 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 AUAudioInputStream::HardwareSampleRate() to retrieve the sample rate.
 // - Calling Close() also leads to self destruction.
+// - The latency consists of two parts:
+//   1, Hardware latency, which includes Audio Unit latency, audio device

[henrika (OOO until Aug 14), 2011/10/21 07:27:23]

I would use 1) and 2)

[no longer working on chromium, 2011/10/21 12:21:46]

Done.

+//      latency and audio stream latency;
+//   2, The delay between now and the scheduled time stamp that tells when the

[henrika (OOO until Aug 14), 2011/10/21 07:27:23]

Please rewrite this comment from scratch since it is not clear. I would say
something like: 

"The time difference between the actual recording instant and the time where the
data packet is provided to us as a callback".

[no longer working on chromium, 2011/10/21 12:21:46]

Done.

+//      data we are providing is going to reach the hardware.
 //
 #ifndef MEDIA_AUDIO_MAC_AUDIO_LOW_LATENCY_INPUT_MAC_H_
 #define MEDIA_AUDIO_MAC_AUDIO_LOW_LATENCY_INPUT_MAC_H_
 
 #include <AudioUnit/AudioUnit.h>
 
 #include "base/memory/scoped_ptr.h"
 #include "base/synchronization/lock.h"
 #include "media/audio/audio_io.h"
 #include "media/audio/audio_parameters.h"
@@ skipping 26 matching lines @@
  private:
   // AudioOutputUnit callback.
   static OSStatus InputProc(void* user_data,
                             AudioUnitRenderActionFlags* flags,
                             const AudioTimeStamp* time_stamp,
                             UInt32 bus_number,
                             UInt32 number_of_frames,
                             AudioBufferList* io_data);
 
   // Pushes recorded data to consumer of the input audio stream.
-  OSStatus Provide(UInt32 number_of_frames, AudioBufferList* io_data);
+  OSStatus Provide(UInt32 number_of_frames, AudioBufferList* io_data,
+                   const AudioTimeStamp* time_stamp);
+
+  // Gets the fixed capture hardware latency and store it during initialization.
+  // Returns 0 if not available.
+  double GetHardwareLatency();
+
+  // Gets the current capture delay value.
+  double GetCaptureLatency(const AudioTimeStamp* input_time_stamp);
 
   // Issues the OnError() callback to the |sink_|.
   void HandleError(OSStatus err);
 
   // Our creator, the audio manager needs to be notified when we close.
   AudioManagerMac* manager_;
 
   // Contains the desired number of audio frames in each callback.
   size_t number_of_frames_;
 
   // Pointer to the object that will receive the recorded audio samples.
   AudioInputCallback* sink_;
 
   // Structure that holds the desired output format of the stream.
   // Note that, this format can differ from the device(=input) format.
   AudioStreamBasicDescription format_;
 
   // The special Audio Unit called AUHAL, which allows us to pass audio data
   // directly from a microphone, through the HAL, and to our application.
   // The AUHAL also enables selection of non default devices.
   AudioUnit audio_unit_;
 
+  // The UID refers to the current input audio device.
+  AudioDeviceID input_device_id_;
+
   // Provides a mechanism for encapsulating one or more buffers of audio data.
   AudioBufferList audio_buffer_list_;
 
   // Temporary storage for recorded data. The InputProc() renders into this
   // array as soon as a frame of the desired buffer size has been recorded.
   scoped_array<uint8> audio_data_buffer_;
 
   // True after successfull Start(), false after successful Stop().
   bool started_;
 
+  // Fixed capture hardware latency in frames.
+  double hardware_latency_frames_;
+
   DISALLOW_COPY_AND_ASSIGN(AUAudioInputStream);
 };
 
 #endif  // MEDIA_AUDIO_MAC_AUDIO_LOW_LATENCY_INPUT_MAC_H_