Browser-wide audio mirroring for TabCapture API

media/audio/audio_output_resampler.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.
 
 #ifndef MEDIA_AUDIO_AUDIO_OUTPUT_RESAMPLER_H_
 #define MEDIA_AUDIO_AUDIO_OUTPUT_RESAMPLER_H_
 
 #include <map>
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
+#include "base/message_loop.h"
 #include "base/time.h"
 #include "media/audio/audio_io.h"
 #include "media/audio/audio_manager.h"
 #include "media/audio/audio_output_dispatcher.h"
 #include "media/audio/audio_parameters.h"
+#include "media/base/audio_pull_fifo.h"
+#include "media/base/channel_mixer.h"
+#include "media/base/multi_channel_resampler.h"
 
 namespace media {
 
-class OnMoreDataResampler;
+class OnMoreDataResampler : public AudioOutputStream::AudioSourceCallback {
+ public:
+  OnMoreDataResampler(double io_ratio,
+                      const AudioParameters& input_params,
+                      const AudioParameters& output_params);
+  virtual ~OnMoreDataResampler();
+
+  // AudioSourceCallback interface.
+  virtual int OnMoreData(AudioBus* dest,
+                         AudioBuffersState buffers_state) OVERRIDE;
+  virtual int OnMoreIOData(AudioBus* source,
+                           AudioBus* dest,
+                           AudioBuffersState buffers_state) OVERRIDE;
+  virtual void OnError(AudioOutputStream* stream, int code) OVERRIDE;
+  virtual void WaitTillDataReady() OVERRIDE;
+
+  // Sets |source_callback_|.  If this is not a new object, then Stop() must be
+  // called before Start().
+  void Start(AudioOutputStream::AudioSourceCallback* callback);
+
+  // Clears |source_callback_| and flushes the resampler.
+  void Stop();
+
+ private:
+  // Called by MultiChannelResampler when more data is necessary.
+  void ProvideInput(AudioBus* audio_bus);
+
+  // Called by AudioPullFifo when more data is necessary.  Requires
+  // |source_lock_| to have been acquired.
+  void SourceCallback_Locked(AudioBus* audio_bus);
+
+  // Passes through |source| to the |source_callback_| OnMoreIOData() call.
+  void SourceIOCallback_Locked(AudioBus* source, AudioBus* dest);
+
+  // Ratio of input bytes to output bytes used to correct playback delay with
+  // regard to buffering and resampling.
+  double io_ratio_;
+
+  // Source callback and associated lock.
+  base::Lock source_lock_;
+  AudioOutputStream::AudioSourceCallback* source_callback_;
+
+  // Last AudioBuffersState object received via OnMoreData(), used to correct
+  // playback delay by ProvideInput() and passed on to |source_callback_|.
+  AudioBuffersState current_buffers_state_;
+
+  // Total number of bytes (in terms of output parameters) stored in resampler
+  // or FIFO buffers which have not been sent to the audio device.
+  int outstanding_audio_bytes_;
+
+  // Used to buffer data between the client and the output device in cases where
+  // the client buffer size is not the same as the output device buffer size.
+  // Bound to SourceCallback_Locked() so must only be used when |source_lock_|
+  // has already been acquired.
+  scoped_ptr<AudioPullFifo> audio_fifo_;
+
+  // Handles resampling.
+  scoped_ptr<MultiChannelResampler> resampler_;
+
+  // Handles channel transforms.  |unmixed_audio_| is a temporary destination
+  // for audio data before it goes into the channel mixer.
+  scoped_ptr<ChannelMixer> channel_mixer_;
+  scoped_ptr<AudioBus> unmixed_audio_;
+
+  int output_bytes_per_frame_;
+  int input_bytes_per_frame_;
+
+  // Since resampling is expensive, figure out if we should downmix channels
+  // before resampling.
+  bool downmix_early_;
+
+  DISALLOW_COPY_AND_ASSIGN(OnMoreDataResampler);
+};
 
 // AudioOutputResampler is a browser-side resampling and rebuffering solution
 // which ensures audio data is always output at given parameters.  The rough
 // flow is: Client -> [FIFO] -> [Resampler] -> Output Device.
 //
 // The FIFO and resampler are only used when necessary.  To be clear:
 //   - The resampler is only used if the input and output sample rates differ.
 //   - The FIFO is only used if the input and output frame sizes differ or if
 //     the resampler is used.
 //
@@ skipping 56 matching lines @@
   // Whether any streams have been opened through |dispatcher_|, if so we can't
   // fallback on future OpenStream() failures.
   bool streams_opened_;
 
   DISALLOW_COPY_AND_ASSIGN(AudioOutputResampler);
 };
 
 }  // namespace media
 
 #endif  // MEDIA_AUDIO_AUDIO_OUTPUT_RESAMPLER_H_