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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 #ifndef MEDIA_AUDIO_VIRTUAL_AUDIO_OUTPUT_STREAM_H_
      6 #define MEDIA_AUDIO_VIRTUAL_AUDIO_OUTPUT_STREAM_H_
      7 
      8 #include "base/callback.h"
      9 #include "base/threading/thread_checker.h"
     10 #include "media/audio/audio_io.h"
     11 #include "media/audio/audio_parameters.h"
     12 #include "media/base/audio_converter.h"
     13 
     14 namespace media {
     15 
     16 class VirtualAudioInputStream;
     17 
     18 // VirtualAudioOutputStream attaches to a VirtualAudioInputStream when Start()
     19 // is called and is used as an audio source. VirtualAudioOutputStream also
     20 // implements an interface so it can be used as an input to AudioConverter so
     21 // that we can get audio frames that match the AudioParameters that
     22 // VirtualAudioInputStream expects.
     23 class MEDIA_EXPORT VirtualAudioOutputStream
     24     : public AudioOutputStream,
     25       public AudioConverter::InputCallback {
     26  public:
     27   // Callback invoked just after VirtualAudioOutputStream is closed.
     28   typedef base::Callback<void(VirtualAudioOutputStream* vaos)>
     29       AfterCloseCallback;
     30 
     31   // Construct an audio loopback pathway to the given |target| (not owned).
     32   // |target| must outlive this instance.
     33   VirtualAudioOutputStream(const AudioParameters& params,
     34                            VirtualAudioInputStream* target,
     35                            const AfterCloseCallback& after_close_cb);
     36 
     37   virtual ~VirtualAudioOutputStream();
     38 
     39   // AudioOutputStream:
     40   virtual bool Open() OVERRIDE;
     41   virtual void Start(AudioSourceCallback* callback) OVERRIDE;
     42   virtual void Stop() OVERRIDE;
     43   virtual void SetVolume(double volume) OVERRIDE;
     44   virtual void GetVolume(double* volume) OVERRIDE;
     45   virtual void Close() OVERRIDE;
     46 
     47  private:
     48   // AudioConverter::InputCallback:
     49   virtual double ProvideInput(AudioBus* audio_bus,
     50                               base::TimeDelta buffer_delay) OVERRIDE;
     51 
     52   const AudioParameters params_;
     53   // Pointer to the VirtualAudioInputStream to attach to when Start() is called.
     54   // This pointer should always be valid because VirtualAudioInputStream should
     55   // outlive this class.
     56   VirtualAudioInputStream* const target_input_stream_;
     57 
     58   AfterCloseCallback after_close_cb_;
     59 
     60   AudioSourceCallback* callback_;
     61   double volume_;
     62 
     63   base::ThreadChecker thread_checker_;
     64 
     65   DISALLOW_COPY_AND_ASSIGN(VirtualAudioOutputStream);
     66 };
     67 
     68 }  // namespace media
     69 
     70 #endif  // MEDIA_AUDIO_VIRTUAL_AUDIO_OUTPUT_STREAM_H_
     71