Add MultiChannelResampler wrapper for SincResampler.

media/base/multi_channel_resampler.cc

Index: media/base/multi_channel_resampler.cc
diff --git a/media/base/multi_channel_resampler.cc b/media/base/multi_channel_resampler.cc
new file mode 100644
index 0000000000000000000000000000000000000000..23479b13b7be4574edf73a1e51b19b22b40cd56c
--- /dev/null
+++ b/media/base/multi_channel_resampler.cc
@@ -0,0 +1,93 @@
+// 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),
+      callback_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(

[Ami GONE FROM CHROMIUM, 2012/07/03 18:53:12]

multi-line for bodies require braces

[DaleCurtis, 2012/07/04 00:56:19]

Done.

+        base::Bind(

[Ami GONE FROM CHROMIUM, 2012/07/03 18:53:12]

could go on prev line

[DaleCurtis, 2012/07/04 00:56:19]

Done.

+            &MultiChannelResampler::ProvideInput, base::Unretained(this), i),
+        io_sample_rate_ratio));
+
+  // Preallocate staging arrays based on SincResampler's buffer size.
+  resampler_audio_data_.reserve(channels);
+  for (int i = 0; i < channels; ++i)
+    resampler_audio_data_.push_back(new float[SincResampler::kBufferSize]);
+}
+
+MultiChannelResampler::~MultiChannelResampler() {
+  // Clean up |resampler_audio_data_|.
+  for (size_t i = 0; 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());
+  DCHECK_EQ(destination.size(), resampler_audio_data_.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::kBlockSize chunks for which SincResampler guarantees it will
+  // only call ProvideInput() once.
+  int frames_done = 0;
+  while (frames_done < frames) {
+    int frames_this_time = std::min(
+        frames - frames_done, static_cast<int>(SincResampler::kBlockSize));
+
+    // Sanity check to ensure ProvideInput() is only called once per channel.
+    callback_count_ = 0;
+
+    // Resample each channel.
+    for (size_t i = 0; i < resamplers_.size(); ++i) {
+      // 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) {
+    DCHECK_LE(frames, SincResampler::kBufferSize);
+    last_frame_count_ = frames;
+    read_cb_.Run(resampler_audio_data_, frames);
+  }
+
+  // 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_);
+  DCHECK_EQ(channel, callback_count_++);

[Ami GONE FROM CHROMIUM, 2012/07/03 18:53:12]

I think it's poor form to have a variable that sits at 0 for the lifetime of the
process in Release.  You might just promote this to a CHECK (with a comment
explaining you want the side-effect, always).

[DaleCurtis, 2012/07/04 00:56:19]

Switched to DCHECK and moved ++ out.

+
+  // Copy the channel data from what we received from |provider_|.
+  memcpy(destination, resampler_audio_data_[channel],

[Ami GONE FROM CHROMIUM, 2012/07/03 18:53:12]

It'd be nicer to avoid this copy, but I guess that'd require overhauling SR's
API.

+         sizeof(*resampler_audio_data_[channel]) * frames);
+}
+
+}  // namespace media