(Committing on behalf of Chris Rogers -- original CL...

media/audio/audio_util.cc

 // Copyright (c) 2010 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.
 
 // Software adjust volume of samples, allows each audio stream its own
 // volume without impacting master volume for chrome and other applications.
 
 // Implemented as templates to allow 8, 16 and 32 bit implementations.
 // 8 bit is unsigned and biased by 128.
 
@@ skipping 140 matching lines @@
           reinterpret_cast<int32*>(buf),
           sample_count,
           volume,
           channels);
       return true;
     }
   }
   return false;
 }
 
+bool DeinterleaveAudioChannel(void* source,
+                              float* destination,
+                              int channels,
+                              int channel_index,
+                              int bytes_per_sample,
+                              size_t number_of_frames) {
+  switch (bytes_per_sample) {
+    case 1:
+    {
+      uint8* source8 = static_cast<uint8*>(source) + channel_index;
+      const float kScale = 1.0f / 128.0f;
+      for (unsigned i = 0; i < number_of_frames; ++i) {
+        destination[i] = kScale * static_cast<int>(*source8 + 128);
+        source8 += channels;
+      }
+      return true;
+    }
+
+    case 2:
+    {
+      int16* source16 = static_cast<int16*>(source) + channel_index;
+      const float kScale = 1.0f / 32768.0f;
+      for (unsigned i = 0; i < number_of_frames; ++i) {
+        destination[i] = kScale * *source16;
+        source16 += channels;
+      }
+      return true;
+    }
+
+    case 4:
+    {
+      int32* source32 = static_cast<int32*>(source) + channel_index;
+      const float kScale = 1.0f / (1L << 31);
+      for (unsigned i = 0; i < number_of_frames; ++i) {
+        destination[i] = kScale * *source32;
+        source32 += channels;
+      }
+      return true;
+    }
+
+    default:
+     break;
+  }
+  return false;
+}
+
 }  // namespace media