Add SincResampler ported from WebKit.

media/base/sinc_resampler.h

+// Copyright (c) 2012 The Chromium Authors. All rights reserved.

[Ami GONE FROM CHROMIUM, 2012/06/30 20:29:30]

Visual plot link should include a bit of explanation about it means, and ideally
hosted someplace public (gdoc / imgur / whatever).

[DaleCurtis, 2012/07/03 00:36:34]

Moved to imgur and updated description.

+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef MEDIA_BASE_SINC_RESAMPLER_H_
+#define MEDIA_BASE_SINC_RESAMPLER_H_
+
+#include "media/base/media_export.h"
+
+namespace media {
+
+// SincResampler is a high-quality single-channel sample-rate converter.
+class MEDIA_EXPORT SincResampler {
+ public:
+  // The number of destination frames generated per processing pass.
+  static const int kBlockSize;

[Ami GONE FROM CHROMIUM, 2012/06/30 20:29:30]

enum turns this into a compile-time constant, avoids storage, and allows
specifying the value right here (easier to find than in .cc file).

[DaleCurtis, 2012/07/03 00:36:34]

With the changes to multichannel resampler, these won't need to be public.

[DaleCurtis, 2012/07/03 01:53:07]

Actually this is more complicated than I thought, I think the current MCR
implementation is clearer, so I've put these back as enum.

+
+  // The size of the internal buffer used by the resampler.
+  static const int kBufferSize;

[Ami GONE FROM CHROMIUM, 2012/06/30 20:29:30]

ditto

[DaleCurtis, 2012/07/03 00:36:34]

Ditto.

+
+  // Abstract base-class for a pulling data into SincResampler.

[Ami GONE FROM CHROMIUM, 2012/06/30 20:29:30]

Ditto to comment from other CL; make this a typedef CB.

[DaleCurtis, 2012/07/03 00:36:34]

Done.

+  class AudioSourceProvider {
+   public:
+    // ProvideInput() is called repeatedly to render time-slices of a continuous
+    // audio stream.
+    virtual void ProvideInput(float* destination, int number_of_frames) = 0;
+
+   protected:
+    virtual ~AudioSourceProvider() {}
+  };
+
+  // Constructs a SincResampler with the specified |provider|, which is used to
+  // acquire audio data for resampling.  |scale_factor| is input_sample_rate /
+  // output_sample_rate.
+  // TODO(dalecurtis): Should provider be a const ref? Need to make ProvideInput
+  // const if so... Following the RenderCallback model currently.
+  SincResampler(AudioSourceProvider* provider, double scale_factor);
+  virtual ~SincResampler();
+
+  // Resample |number_of_frames| of data from |provider_| into |destination|.
+  // If |number_of_frames| < kBlockSize AudioSourceProvider::ProvideInput() will
+  // be called at most once depending on if data remains in the internal buffer.
+  void Resample(float* destination, int number_of_frames);
+
+ private:
+  double scale_factor_;
+
+  // |virtual_source_idx_| is an index on the source input buffer with
+  // sub-sample precision.  It must be double precision to avoid drift.
+  double virtual_source_idx_;
+
+  // The buffer is primed once at the very beginning of processing.
+  bool buffer_primed_;
+
+  // |provider_| is used to provide the audio input stream to the resampler.
+  AudioSourceProvider* provider_;
+
+  // |kernel_storage_| has kKernelOffsetCount kernels back-to-back, each of size
+  // kKernelSize.  The kernel offsets are sub-sample shifts of a windowed sinc
+  // shifted from 0.0 to 1.0 sample.
+  float* kernel_storage_;

[Ami GONE FROM CHROMIUM, 2012/06/30 20:29:30]

scoped

[DaleCurtis, 2012/07/03 00:36:34]

Done.

+
+  // Data from the source is copied into this buffer for each processing pass.
+  float* input_buffer_;

[Ami GONE FROM CHROMIUM, 2012/06/30 20:29:30]

scoped

[DaleCurtis, 2012/07/03 00:36:34]

Done.

+
+  void InitializeKernel();
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_SINC_RESAMPLER_H_