Adding input and output delay estimation for mac.

media/audio/mac/audio_low_latency_input_mac.h

Index: media/audio/mac/audio_low_latency_input_mac.h
===================================================================
--- media/audio/mac/audio_low_latency_input_mac.h	(revision 106304)
+++ media/audio/mac/audio_low_latency_input_mac.h	(working copy)
@@ -27,6 +27,11 @@
 //   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_
@@ -73,8 +78,16 @@
                             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);
 
@@ -96,6 +109,9 @@
   // 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_;
 
@@ -106,6 +122,9 @@
   // 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);
 };