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      1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
      2 // Use of this source code is governed by a BSD-style license that can be
      3 // found in the LICENSE file.
      4 //
      5 // Implementation notes:
      6 //
      7 // - It is recommended to first acquire the native sample rate of the default
      8 //   output device and then use the same rate when creating this object.
      9 //   Use AUAudioOutputStream::HardwareSampleRate() to retrieve the sample rate.
     10 // - Calling Close() also leads to self destruction.
     11 // - The latency consists of two parts:
     12 //   1) Hardware latency, which includes Audio Unit latency, audio device
     13 //      latency;
     14 //   2) The delay between the moment getting the callback and the scheduled time
     15 //      stamp that tells when the data is going to be played out.
     16 //
     17 #ifndef MEDIA_AUDIO_MAC_AUDIO_LOW_LATENCY_OUTPUT_MAC_H_
     18 #define MEDIA_AUDIO_MAC_AUDIO_LOW_LATENCY_OUTPUT_MAC_H_
     19 
     20 #include <AudioUnit/AudioUnit.h>
     21 #include <CoreAudio/CoreAudio.h>
     22 
     23 #include "base/compiler_specific.h"
     24 #include "base/synchronization/lock.h"
     25 #include "media/audio/audio_io.h"
     26 #include "media/audio/audio_parameters.h"
     27 
     28 namespace media {
     29 
     30 class AudioManagerMac;
     31 
     32 // Implementation of AudioOuputStream for Mac OS X using the
     33 // default output Audio Unit present in OS 10.4 and later.
     34 // The default output Audio Unit is for low-latency audio I/O.
     35 class AUAudioOutputStream : public AudioOutputStream {
     36  public:
     37   // The ctor takes all the usual parameters, plus |manager| which is the
     38   // the audio manager who is creating this object.
     39   AUAudioOutputStream(AudioManagerMac* manager,
     40                       const AudioParameters& params);
     41   // The dtor is typically called by the AudioManager only and it is usually
     42   // triggered by calling AudioOutputStream::Close().
     43   virtual ~AUAudioOutputStream();
     44 
     45   // Implementation of AudioOutputStream.
     46   virtual bool Open() OVERRIDE;
     47   virtual void Close() OVERRIDE;
     48   virtual void Start(AudioSourceCallback* callback) OVERRIDE;
     49   virtual void Stop() OVERRIDE;
     50   virtual void SetVolume(double volume) OVERRIDE;
     51   virtual void GetVolume(double* volume) OVERRIDE;
     52 
     53   static int HardwareSampleRate();
     54 
     55  private:
     56   // DefaultOutputUnit callback.
     57   static OSStatus InputProc(void* user_data,
     58                             AudioUnitRenderActionFlags* flags,
     59                             const AudioTimeStamp* time_stamp,
     60                             UInt32 bus_number,
     61                             UInt32 number_of_frames,
     62                             AudioBufferList* io_data);
     63 
     64   OSStatus Render(UInt32 number_of_frames, AudioBufferList* io_data,
     65                   const AudioTimeStamp* output_time_stamp);
     66 
     67   // Sets up the stream format for the default output Audio Unit.
     68   bool Configure();
     69 
     70   // Gets the fixed playout device hardware latency and stores it. Returns 0
     71   // if not available.
     72   double GetHardwareLatency();
     73 
     74   // Gets the current playout latency value.
     75   double GetPlayoutLatency(const AudioTimeStamp* output_time_stamp);
     76 
     77   // Our creator, the audio manager needs to be notified when we close.
     78   AudioManagerMac* manager_;
     79 
     80   size_t number_of_frames_;
     81 
     82   // Pointer to the object that will provide the audio samples.
     83   AudioSourceCallback* source_;
     84 
     85   // Protects |source_|.  Necessary since Render() calls seem to be in flight
     86   // when |output_unit_| is supposedly stopped.  See http://crbug.com/178765.
     87   base::Lock source_lock_;
     88 
     89   // Structure that holds the stream format details such as bitrate.
     90   AudioStreamBasicDescription format_;
     91 
     92   // The default output Audio Unit which talks to the audio hardware.
     93   AudioUnit output_unit_;
     94 
     95   // The UID refers to the current output audio device.
     96   AudioDeviceID output_device_id_;
     97 
     98   // Volume level from 0 to 1.
     99   float volume_;
    100 
    101   // Fixed playout hardware latency in frames.
    102   double hardware_latency_frames_;
    103 
    104   // The flag used to stop the streaming.
    105   bool stopped_;
    106 
    107   // Container for retrieving data from AudioSourceCallback::OnMoreData().
    108   scoped_ptr<AudioBus> audio_bus_;
    109 
    110   DISALLOW_COPY_AND_ASSIGN(AUAudioOutputStream);
    111 };
    112 
    113 }  // namespace media
    114 
    115 #endif  // MEDIA_AUDIO_MAC_AUDIO_LOW_LATENCY_OUTPUT_MAC_H_
    116