Add MultiChannelResampler wrapper for SincResampler.

media/base/multi_channel_resampler.cc

+// 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.
+
+#include "media/base/multi_channel_resampler.h"
+
+#include "base/bind.h"
+#include "base/bind_helpers.h"
+#include "base/logging.h"
+
+namespace media {
+
+MultiChannelResampler::MultiChannelResampler(int channels,
+                                             double io_sample_rate_ratio,
+                                             const ReadCB& read_cb)
+    : last_frame_count_(0),
+      first_frame_count_(0),
+      read_cb_(read_cb) {
+  // Allocate each channel's resampler.
+  resamplers_.reserve(channels);
+  for (int i = 0; i < channels; ++i) {
+    resamplers_.push_back(new SincResampler(io_sample_rate_ratio, base::Bind(
+        &MultiChannelResampler::ProvideInput, base::Unretained(this), i)));
+  }
+}
+
+MultiChannelResampler::~MultiChannelResampler() {
+  // Clean up |resampler_audio_data_|.  Skip the first channel since we never
+  // allocated that, but just used the destination passed into ProvideInput().
+  for (size_t i = 1; i < resampler_audio_data_.size(); ++i)
+    delete [] resampler_audio_data_[i];
+  resampler_audio_data_.clear();
+}
+
+void MultiChannelResampler::Resample(const std::vector<float*>& destination,
+                                     int frames) {
+  DCHECK_EQ(destination.size(), resamplers_.size());
+
+  // We need to ensure that SincResampler only calls ProvideInput once for each
+  // channel.  To ensure this, we chunk the number of requested frames into
+  // SincResampler::ChunkSize() sized chunks.  SincResampler guarantees it will
+  // only call ProvideInput() once when we resample this way.
+  int frames_done = 0;
+  int chunk_size = resamplers_[0]->ChunkSize();
+  while (frames_done < frames) {
+    int frames_this_time = std::min(frames - frames_done, chunk_size);
+
+    // Resample each channel.
+    for (size_t i = 0; i < resamplers_.size(); ++i) {
+      DCHECK_EQ(chunk_size, resamplers_[i]->ChunkSize());
+
+      // Depending on the sample-rate scale factor, and the internal buffering
+      // used in a SincResampler kernel, this call to Resample() will only
+      // sometimes call ProvideInput().  However, if it calls ProvideInput() for
+      // the first channel, then it will call it for the remaining channels,
+      // since they all buffer in the same way and are processing the same
+      // number of frames.
+      resamplers_[i]->Resample(destination[i] + frames_done, frames_this_time);
+    }
+
+    frames_done += frames_this_time;
+  }
+}
+
+void MultiChannelResampler::ProvideInput(int channel, float* destination,
+                                         int frames) {
+  // Get the data from the multi-channel provider when the first channel asks
+  // for it.  For subsequent channels, we can just dish out the channel data
+  // from that (stored in |resampler_audio_data_|).
+  if (channel == 0) {
+    // Allocate staging arrays on the first request.
+    if (resampler_audio_data_.size() == 0) {
+      first_frame_count_ = frames;
+      // Skip allocation of the first buffer, since we'll use |destination|
+      // directly for that.
+      resampler_audio_data_.reserve(resamplers_.size());
+      resampler_audio_data_.push_back(destination);
+      for (size_t i = 1; i < resamplers_.size(); ++i)
+        resampler_audio_data_.push_back(new float[frames]);
+    } else {
+      DCHECK_LE(frames, first_frame_count_);
+      resampler_audio_data_[0] = destination;
+    }
+
+    last_frame_count_ = frames;
+    read_cb_.Run(resampler_audio_data_, frames);
+  } else {
+    // All channels must ask for the same amount.  This should always be the
+    // case, but let's just make sure.
+    DCHECK_EQ(frames, last_frame_count_);
+
+    // Copy the channel data from what we received from |read_cb_|.
+    memcpy(destination, resampler_audio_data_[channel],
+           sizeof(*resampler_audio_data_[channel]) * frames);
+  }
+}
+
+}  // namespace media