Support 4 channel mic in Windows Core Audio

webrtc/audio/utility/audio_frame_operations.h

Index: webrtc/audio/utility/audio_frame_operations.h
diff --git a/webrtc/audio/utility/audio_frame_operations.h b/webrtc/audio/utility/audio_frame_operations.h
index d16b163e7d1139f10ba00e87e73524648e01bebd..de6fdc472d710074ed603600ce73b8a493165447 100644
--- a/webrtc/audio/utility/audio_frame_operations.h
+++ b/webrtc/audio/utility/audio_frame_operations.h
@@ -40,6 +40,7 @@ class AudioFrameOperations {
   static void MonoToStereo(const int16_t* src_audio,
                            size_t samples_per_channel,
                            int16_t* dst_audio);
+
   // |frame.num_channels_| will be updated. This version checks for sufficient
   // buffer size and that |num_channels_| is mono.
   static int MonoToStereo(AudioFrame* frame);
@@ -50,10 +51,49 @@ class AudioFrameOperations {
   static void StereoToMono(const int16_t* src_audio,
                            size_t samples_per_channel,
                            int16_t* dst_audio);
+
   // |frame.num_channels_| will be updated. This version checks that
   // |num_channels_| is stereo.
   static int StereoToMono(AudioFrame* frame);
 
+  // Downmixes 4 channels |src_audio| to stereo |dst_audio|. This is an in-place
+  // operation, meaning |src_audio| and |dst_audio| may point to the same
+  // buffer.
+  static void QuadToStereo(const int16_t* src_audio,
+                           size_t samples_per_channel,
+                           int16_t* dst_audio);
+
+  // |frame.num_channels_| will be updated. This version checks that
+  // |num_channels_| is 4 channels.
+  static int QuadToStereo(AudioFrame* frame);
+
+  // Downmixes 4 channels |src_audio| to mono |dst_audio|. This is an in-place
+  // operation, meaning |src_audio| and |dst_audio| may point to the same
+  // buffer.
+  static void QuadToMono(const int16_t* src_audio,
+                         size_t samples_per_channel,
+                         int16_t* dst_audio);
+
+  // |frame.num_channels_| will be updated. This version checks that
+  // |num_channels_| is 4 channels.
+  static int QuadToMono(AudioFrame* frame);
+
+  // Downmixes |src_channels| |src_audio| to |dst_channels| |dst_audio|.
+  // This is an in-place operation, meaning |src_audio| and |dst_audio|
+  // may point to the same buffer. Supported channel combinations are
+  // Stereo to Mono, Quad to Mono, and Quad to Stereo.
+  static void DownmixChannels(const int16_t* src_audio,
+                              size_t src_channels,
+                              size_t samples_per_channel,
+                              size_t dst_channels,
+                              int16_t* dst_audio);
+
+  // |frame.num_channels_| will be updated. This version checks that
+  // |num_channels_| and |dst_channels| are valid and performs relevant
+  // downmix.  Supported channel combinations are Stereo to Mono, Quad to Mono,
+  // and Quad to Stereo.
+  static int DownmixChannels(size_t dst_channels, AudioFrame* frame);
+
   // Swap the left and right channels of |frame|. Fails silently if |frame| is
   // not stereo.
   static void SwapStereoChannels(AudioFrame* frame);