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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_BASE_MULTI_CHANNEL_RESAMPLER_H_
      6 #define MEDIA_BASE_MULTI_CHANNEL_RESAMPLER_H_
      7 
      8 #include <vector>
      9 
     10 #include "base/callback.h"
     11 #include "base/memory/scoped_ptr.h"
     12 #include "base/memory/scoped_vector.h"
     13 #include "media/base/sinc_resampler.h"
     14 
     15 namespace media {
     16 class AudioBus;
     17 
     18 // MultiChannelResampler is a multi channel wrapper for SincResampler; allowing
     19 // high quality sample rate conversion of multiple channels at once.
     20 class MEDIA_EXPORT MultiChannelResampler {
     21  public:
     22   // Callback type for providing more data into the resampler.  Expects AudioBus
     23   // to be completely filled with data upon return; zero padded if not enough
     24   // frames are available to satisfy the request.  |frame_delay| is the number
     25   // of output frames already processed and can be used to estimate delay.
     26   typedef base::Callback<void(int frame_delay, AudioBus* audio_bus)> ReadCB;
     27 
     28   // Constructs a MultiChannelResampler with the specified |read_cb|, which is
     29   // used to acquire audio data for resampling.  |io_sample_rate_ratio| is the
     30   // ratio of input / output sample rates.  |request_frames| is the size in
     31   // frames of the AudioBus to be filled by |read_cb|.
     32   MultiChannelResampler(int channels,
     33                         double io_sample_rate_ratio,
     34                         size_t request_frames,
     35                         const ReadCB& read_cb);
     36   virtual ~MultiChannelResampler();
     37 
     38   // Resamples |frames| of data from |read_cb_| into AudioBus.
     39   void Resample(int frames, AudioBus* audio_bus);
     40 
     41   // Flush all buffered data and reset internal indices.  Not thread safe, do
     42   // not call while Resample() is in progress.
     43   void Flush();
     44 
     45   // Update ratio for all SincResamplers.  SetRatio() will cause reconstruction
     46   // of the kernels used for resampling.  Not thread safe, do not call while
     47   // Resample() is in progress.
     48   void SetRatio(double io_sample_rate_ratio);
     49 
     50  private:
     51   // SincResampler::ReadCB implementation.  ProvideInput() will be called for
     52   // each channel (in channel order) as SincResampler needs more data.
     53   void ProvideInput(int channel, int frames, float* destination);
     54 
     55   // Source of data for resampling.
     56   ReadCB read_cb_;
     57 
     58   // Each channel has its own high quality resampler.
     59   ScopedVector<SincResampler> resamplers_;
     60 
     61   // Buffers for audio data going into SincResampler from ReadCB.
     62   scoped_ptr<AudioBus> resampler_audio_bus_;
     63 
     64   // To avoid a memcpy() on the first channel we create a wrapped AudioBus where
     65   // the first channel points to the |destination| provided to ProvideInput().
     66   scoped_ptr<AudioBus> wrapped_resampler_audio_bus_;
     67 
     68   // The number of output frames that have successfully been processed during
     69   // the current Resample() call.
     70   int output_frames_ready_;
     71 
     72   DISALLOW_COPY_AND_ASSIGN(MultiChannelResampler);
     73 };
     74 
     75 }  // namespace media
     76 
     77 #endif  // MEDIA_BASE_MULTI_CHANNEL_RESAMPLER_H_
     78