Add SincResampler ported from WebKit.

media/base/sinc_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_BASE_SINC_RESAMPLER_H_
+#define MEDIA_BASE_SINC_RESAMPLER_H_
+
+#include "base/callback.h"
+#include "base/memory/scoped_ptr.h"
+#include "media/base/media_export.h"
+
+namespace media {
+
+// SincResampler is a high-quality single-channel sample-rate converter.
+class MEDIA_EXPORT SincResampler {
+ public:
+  enum {
+    // The kernel size can be adjusted for quality (higher is better).

[Ami GONE FROM CHROMIUM, 2012/07/03 20:54:42]

For each of these magic constants you should state the tradeoff (why not use
kint32max/0/kint32min?).

[DaleCurtis, 2012/07/10 01:00:25]

Done.

+    // TODO(dalecurtis): Test performance to see if we can jack this up to 64+.
+    kKernelSize = 32,
+
+    // The number of destination frames generated per processing pass.
+    kBlockSize = 512,
+
+    // The kernel offset count is used for interpolation and is the number of
+    // sub-sample kernel shifts.
+    kKernelOffsetCount = 32,
+    kKernelStorageSize = kKernelSize * (kKernelOffsetCount + 1),
+
+    // The size of the internal buffer used by the resampler.

[Ami GONE FROM CHROMIUM, 2012/07/03 20:54:42]

If this is the only thing that needs to be public can you remove the rest of the
public: section?

[Ami GONE FROM CHROMIUM, 2012/07/03 20:54:42]

"size" here means frame count, right?  Clarify here and above.
But really I think the part of this that you want to actually make part of the
public API is *not* the "internal buffer size" but rather "Frame count below
which clients are guaranteed read_cb_ will be called no more than once".

[DaleCurtis, 2012/07/09 20:35:34]

Not quite. WDYT about adding a method like:

// Resample up to |frames| of data as can be processed from a single call to
// |read_cb_|.  Returns the number of frames actually processed.  Must be
// called repeatedly with a |frames| value decreased by the number of frames
// returned by the last call to ChunkedResample() to
int ChunkedResample(float* destination, int frames);

Then MCR can just call this repeatedly without having to worry about internal
details of SincResampler.

[DaleCurtis, 2012/07/10 01:00:25]

After discussion with Chris, added a ChunkSize() method which can be used by MCR
without having to know about all this stuff.

+    kBufferSize = kBlockSize + kKernelSize
+  };
+
+  // Callback type for providing more data into the resampler.  Expects |frames|
+  // of data for all channels to be rendered into |destination|; zero padded if

[Ami GONE FROM CHROMIUM, 2012/07/03 20:54:42]

de-multi-channel this comment

[DaleCurtis, 2012/07/10 01:00:25]

Done.

+  // not enough frames are available to satisfy the request.
+  typedef base::Callback<void(float* destination, int frames)> ReadCB;
+
+  // Constructs a SincResampler with the specified |read_cb|, which is used to
+  // acquire audio data for resampling.  |io_sample_rate_ratio| is the ratio of
+  // input / output sample rates.
+  SincResampler(const ReadCB& read_cb, double io_sample_rate_ratio);

[Ami GONE FROM CHROMIUM, 2012/07/03 20:54:42]

I'd put the ratio before the CB.

[DaleCurtis, 2012/07/10 01:00:25]

Done.

+  virtual ~SincResampler();
+
+  // Resample |frames| of data from |read_cb_| into |destination|.
+  void Resample(float* destination, int frames);
+
+ private:
+  // The ratio of input / output sample rates.
+  double io_sample_rate_ratio_;
+
+  // 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_;
+
+  // Source of data for resampling.
+  ReadCB read_cb_;
+
+  // Contains 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.
+  scoped_array<float> kernel_storage_;
+
+  // Data from the source is copied into this buffer for each processing pass.
+  scoped_array<float> input_buffer_;
+
+  void InitializeKernel();
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_SINC_RESAMPLER_H_