Fix slow playback of 1-channel MP3 and AAC files for WebAudio on Android

media/base/android/webaudio_media_codec_bridge.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/android/webaudio_media_codec_bridge.h"
 
 #include <errno.h>
 #include <fcntl.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <unistd.h>
 #include <vector>
 
 #include "base/android/jni_android.h"
 #include "base/android/jni_array.h"
 #include "base/android/jni_string.h"
 #include "base/basictypes.h"
 #include "base/logging.h"
 #include "base/posix/eintr_wrapper.h"
+#include "base/stl_util.h"
 #include "jni/WebAudioMediaCodecBridge_jni.h"
 #include "media/base/android/webaudio_media_codec_info.h"
 
 
 using base::android::AttachCurrentThread;
 
 namespace media {
 
 void WebAudioMediaCodecBridge::RunWebAudioMediaCodec(
     base::SharedMemoryHandle encoded_audio_handle,
@@ skipping 111 matching lines @@
            << "  rate = " << sample_rate
            << "  duration = " << duration_microsec << " microsec";
 
   HANDLE_EINTR(write(pcm_output_, &info, sizeof(info)));
 }
 
 void WebAudioMediaCodecBridge::OnChunkDecoded(
     JNIEnv* env,
     jobject /*java object*/,
     jobject buf,
-    jint buf_size) {
+    jint buf_size,
+    jint input_channel_count,
+    jint output_channel_count) {
 
   if (buf_size <= 0 || !buf)
     return;
 
   int8_t* buffer =
       static_cast<int8_t*>(env->GetDirectBufferAddress(buf));
+  size_t count = static_cast<size_t>(buf_size);
+  std::vector<int16_t> decoded_data;
 
-  size_t count = static_cast<size_t>(buf_size);
+  if (input_channel_count == 1 && output_channel_count == 2) {
+    // See crbug.com/266006.  The file has one channel, but the
+    // decoder decided to return two channels.  To be consistent with
+    // the number of channels in the file, only send one channel (the
+    // first).
+    int16_t* data = static_cast<int16_t*>(env->GetDirectBufferAddress(buf));
+    int frame_count  = buf_size / sizeof(*data) / 2;
+
+    decoded_data.resize(frame_count);
+    for (int k = 0; k < frame_count; ++k) {
+      decoded_data[k] = *data;
+      data += 2;
+    }
+    buffer = reinterpret_cast<int8_t*>(vector_as_array(&decoded_data));
+    DCHECK(buffer);
+    count = frame_count * sizeof(*data);
+  }
 
   // Write out the data to the pipe in small chunks if necessary.
   while (count > 0) {
     int bytes_to_write = (count >= PIPE_BUF) ? PIPE_BUF : count;
     ssize_t bytes_written = HANDLE_EINTR(write(pcm_output_,
                                                buffer,
                                                bytes_to_write));
     if (bytes_written == -1)
       break;
     count -= bytes_written;
     buffer += bytes_written;
   }
 }
 
 bool WebAudioMediaCodecBridge::RegisterWebAudioMediaCodecBridge(JNIEnv* env) {
   return RegisterNativesImpl(env);
 }
 
 } // namespace