Add MultiChannelResampler wrapper for SincResampler.

media/base/multi_channel_resampler.h

Index: media/base/multi_channel_resampler.h
diff --git a/media/base/multi_channel_resampler.h b/media/base/multi_channel_resampler.h
new file mode 100644
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+++ b/media/base/multi_channel_resampler.h
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+// 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_MULTI_CHANNEL_RESAMPLER_H_
+#define MEDIA_BASE_MULTI_CHANNEL_RESAMPLER_H_
+
+#include <vector>
+
+#include "base/callback.h"
+#include "base/memory/scoped_ptr.h"
+#include "base/memory/scoped_vector.h"
+#include "media/base/sinc_resampler.h"
+
+namespace media {
+
+// MultiChannelResampler is a multi channel wrapper for SincResampler; allowing
+// high quality sample rate conversion of multiple channels at once.
+class MEDIA_EXPORT MultiChannelResampler {
+ public:
+  // Callback type for providing more data into the resampler.  Expects |frames|
+  // of data for all channels to be rendered into |destination|; zero padded if
+  // not enough frames are available to satisfy the request.
+  typedef base::Callback<void(const std::vector<float*>& destination,
+                              int frames)> ReadCB;
+
+  // Constructs a MultiChannelResampler 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.
+  MultiChannelResampler(int channels, double io_sample_rate_ratio,
+                        const ReadCB& read_cb);
+  virtual ~MultiChannelResampler();
+
+  // Resample |frames| of data from |read_cb_| into |destination|.
+  void Resample(const std::vector<float*>& destination, int frames);
+
+ private:
+  // Sanity check to ensure that ProvideInput() retrieves the same number of
+  // frames for every channel.
+  int last_frame_count_;
+
+  // Sanity check to ensure ProvideInput() is only called once per channel.
+  int callback_count_;
+
+  // Source of data for resampling.
+  ReadCB read_cb_;
+
+  // Each channel has its own high quality resampler.
+  ScopedVector<SincResampler> resamplers_;
+
+  // Buffer for audio data going into SincResampler from ReadCB.  Owned by this
+  // class and only temporarily passed out to ReadCB when data is required.
+  std::vector<float*> resampler_audio_data_;
+
+  // SincResampler::ReadCB implementation.  ProvideInput() will be called for
+  // each channel (in channel order) as SincResampler needs more data.
+  void ProvideInput(int channel, float* destination, int frames);
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_MULTI_CHANNEL_RESAMPLER_H_