Revert of Allow more than 2 input channels in AudioProcessing.

webrtc/modules/audio_processing/audio_buffer.cc

Index: webrtc/modules/audio_processing/audio_buffer.cc
diff --git a/webrtc/modules/audio_processing/audio_buffer.cc b/webrtc/modules/audio_processing/audio_buffer.cc
index 9073ad7569732a8e9c204b93689c30be86275709..04dcaea799d60af6bbc48d899e9ded8134d6ce03 100644
--- a/webrtc/modules/audio_processing/audio_buffer.cc
+++ b/webrtc/modules/audio_processing/audio_buffer.cc
@@ -23,13 +23,39 @@
 const int kSamplesPer32kHzChannel = 320;
 const int kSamplesPer48kHzChannel = 480;
 
-int KeyboardChannelIndex(const StreamConfig& stream_config) {
-  if (!stream_config.has_keyboard()) {
-    assert(false);
-    return -1;
-  }
-
-  return stream_config.num_channels();
+bool HasKeyboardChannel(AudioProcessing::ChannelLayout layout) {
+  switch (layout) {
+    case AudioProcessing::kMono:
+    case AudioProcessing::kStereo:
+      return false;
+    case AudioProcessing::kMonoAndKeyboard:
+    case AudioProcessing::kStereoAndKeyboard:
+      return true;
+  }
+  assert(false);
+  return false;
+}
+
+int KeyboardChannelIndex(AudioProcessing::ChannelLayout layout) {
+  switch (layout) {
+    case AudioProcessing::kMono:
+    case AudioProcessing::kStereo:
+      assert(false);
+      return -1;
+    case AudioProcessing::kMonoAndKeyboard:
+      return 1;
+    case AudioProcessing::kStereoAndKeyboard:
+      return 2;
+  }
+  assert(false);
+  return -1;
+}
+
+template <typename T>
+void StereoToMono(const T* left, const T* right, T* out,
+                  int num_frames) {
+  for (int i = 0; i < num_frames; ++i)
+    out[i] = (left[i] + right[i]) / 2;
 }
 
 int NumBandsFromSamplesPerChannel(int num_frames) {
@@ -65,7 +91,7 @@
   assert(input_num_frames_ > 0);
   assert(proc_num_frames_ > 0);
   assert(output_num_frames_ > 0);
-  assert(num_input_channels_ > 0);
+  assert(num_input_channels_ > 0 && num_input_channels_ <= 2);
   assert(num_proc_channels_ > 0 && num_proc_channels_ <= num_input_channels_);
 
   if (input_num_frames_ != proc_num_frames_ ||
@@ -104,28 +130,29 @@
 AudioBuffer::~AudioBuffer() {}
 
 void AudioBuffer::CopyFrom(const float* const* data,
-                           const StreamConfig& stream_config) {
-  assert(stream_config.num_frames() == input_num_frames_);
-  assert(stream_config.num_channels() == num_input_channels_);
+                           int num_frames,
+                           AudioProcessing::ChannelLayout layout) {
+  assert(num_frames == input_num_frames_);
+  assert(ChannelsFromLayout(layout) == num_input_channels_);
   InitForNewData();
   // Initialized lazily because there's a different condition in
   // DeinterleaveFrom.
-  const bool need_to_downmix =
-      num_input_channels_ > 1 && num_proc_channels_ == 1;
-  if (need_to_downmix && !input_buffer_) {
+  if ((num_input_channels_ == 2 && num_proc_channels_ == 1) && !input_buffer_) {
     input_buffer_.reset(
         new IFChannelBuffer(input_num_frames_, num_proc_channels_));
   }
 
-  if (stream_config.has_keyboard()) {
-    keyboard_data_ = data[KeyboardChannelIndex(stream_config)];
+  if (HasKeyboardChannel(layout)) {
+    keyboard_data_ = data[KeyboardChannelIndex(layout)];
   }
 
   // Downmix.
   const float* const* data_ptr = data;
-  if (need_to_downmix) {
-    DownmixToMono<float, float>(data, input_num_frames_, num_input_channels_,
-                                input_buffer_->fbuf()->channels()[0]);
+  if (num_input_channels_ == 2 && num_proc_channels_ == 1) {
+    StereoToMono(data[0],
+                 data[1],
+                 input_buffer_->fbuf()->channels()[0],
+                 input_num_frames_);
     data_ptr = input_buffer_->fbuf_const()->channels();
   }
 
@@ -148,10 +175,11 @@
   }
 }
 
-void AudioBuffer::CopyTo(const StreamConfig& stream_config,
+void AudioBuffer::CopyTo(int num_frames,
+                         AudioProcessing::ChannelLayout layout,
                          float* const* data) {
-  assert(stream_config.num_frames() == output_num_frames_);
-  assert(stream_config.num_channels() == num_channels_);
+  assert(num_frames == output_num_frames_);
+  assert(ChannelsFromLayout(layout) == num_channels_);
 
   // Convert to the float range.
   float* const* data_ptr = data;
@@ -299,6 +327,9 @@
 }
 
 const int16_t* AudioBuffer::mixed_low_pass_data() {
+  // Currently only mixing stereo to mono is supported.
+  assert(num_proc_channels_ == 1 || num_proc_channels_ == 2);
+
   if (num_proc_channels_ == 1) {
     return split_bands_const(0)[kBand0To8kHz];
   }
@@ -308,10 +339,10 @@
       mixed_low_pass_channels_.reset(
           new ChannelBuffer<int16_t>(num_split_frames_, 1));
     }
-
-    DownmixToMono<int16_t, int32_t>(split_channels_const(kBand0To8kHz),
-                                    num_split_frames_, num_channels_,
-                                    mixed_low_pass_channels_->channels()[0]);
+    StereoToMono(split_bands_const(0)[kBand0To8kHz],
+                 split_bands_const(1)[kBand0To8kHz],
+                 mixed_low_pass_channels_->channels()[0],
+                 num_split_frames_);
     mixed_low_pass_valid_ = true;
   }
   return mixed_low_pass_channels_->channels()[0];
@@ -380,10 +411,11 @@
   } else {
     deinterleaved = input_buffer_->ibuf()->channels();
   }
-  if (num_proc_channels_ == 1) {
-    // Downmix and deinterleave simultaneously.
-    DownmixInterleavedToMono(frame->data_, input_num_frames_,
-                             num_input_channels_, deinterleaved[0]);
+  if (num_input_channels_ == 2 && num_proc_channels_ == 1) {
+    // Downmix directly; no explicit deinterleaving needed.
+    for (int i = 0; i < input_num_frames_; ++i) {
+      deinterleaved[0][i] = (frame->data_[i * 2] + frame->data_[i * 2 + 1]) / 2;
+    }
   } else {
     assert(num_proc_channels_ == num_input_channels_);
     Deinterleave(frame->data_,