Using native sampling rate and optimal buffer size for audio on Android.

media/audio/android/audio_manager_android.cc

Index: media/audio/android/audio_manager_android.cc
===================================================================
--- media/audio/android/audio_manager_android.cc	(revision 200309)
+++ media/audio/android/audio_manager_android.cc	(working copy)
@@ -56,14 +56,11 @@
 
 AudioParameters AudioManagerAndroid::GetInputStreamParameters(
     const std::string& device_id) {
-  // TODO(xians): figure out the right input sample rate and buffer size to
-  // achieve the best audio performance for Android devices.
-  // TODO(xians): query the native channel layout for the specific device.
-  static const int kDefaultSampleRate = 16000;
   static const int kDefaultBufferSize = 1024;
+  int size = GetMinInputBufferSize(GetNativeOutputSampleRate(), 2);
   return AudioParameters(
       AudioParameters::AUDIO_PCM_LOW_LATENCY, CHANNEL_LAYOUT_STEREO,
-      kDefaultSampleRate, 16, kDefaultBufferSize);
+      GetNativeOutputSampleRate(), 16, size <= 0 ? kDefaultBufferSize : size);
 }
 
 AudioOutputStream* AudioManagerAndroid::MakeAudioOutputStream(
@@ -120,16 +117,24 @@
   return new OpenSLESInputStream(this, params);
 }
 
+int AudioManagerAndroid::GetAudioOptimalOutputFrameSize(int sample_rate,
+                                                        int channels) {
+  if (IsAudioLowLatencySupported()) {
+    const int kTargetFrameSize = 2048;
+    int frame_size = GetAudioLowLatencyFrameSize();
+    // Return the optimal size as a multiple of the low latency frame
+    // size that is close to the target frame size.
+    return ((kTargetFrameSize + frame_size / 2) / frame_size) * frame_size;
+  } else
+    return GetMinOutputBufferSize(sample_rate, channels);

[Raymond Toy (Google), 2013/05/16 04:32:28]

I wonder if we should return the max of GetMinOutputBufferSize and
kTargetFrameSize, in case kTargetFrameSize is too small?

[leozwang2, 2013/05/16 20:56:18]

All devices I have tested have "LowLatency", this else path has not been well
tested. form my experience, this return value might be small for Chromium. 

+}
+
 AudioParameters AudioManagerAndroid::GetPreferredOutputStreamParameters(
     const AudioParameters& input_params) {
-  // TODO(xians): figure out the right output sample rate and buffer size to
-  // achieve the best audio performance for Android devices.
-  static const int kDefaultSampleRate = 44100;
   static const int kDefaultBufferSize = 2048;
-
   ChannelLayout channel_layout = CHANNEL_LAYOUT_STEREO;
-  int sample_rate = kDefaultSampleRate;
-  int buffer_size = kDefaultBufferSize;
+  int sample_rate = GetNativeOutputSampleRate();
+  int buffer_size = GetAudioOptimalOutputFrameSize(sample_rate, 2);
   int bits_per_sample = 16;
   int input_channels = 0;
   if (input_params.IsValid()) {
@@ -138,12 +143,7 @@
     bits_per_sample = input_params.bits_per_sample();
     channel_layout = input_params.channel_layout();
     input_channels = input_params.input_channels();
-
-    // TODO(leozwang): Android defines the minimal buffer size requirment
-    // we should follow it. From Android 4.1, a new audio low latency api
-    // set was introduced and is under development, we want to take advantage
-    // of it.
-    buffer_size = std::min(buffer_size, input_params.frames_per_buffer());
+    buffer_size = buffer_size <= 0 ? kDefaultBufferSize : buffer_size;
   }
 
   int user_buffer_size = GetUserBufferSize();
@@ -178,4 +178,35 @@
       j_audio_manager_.obj());
 }
 
+int AudioManagerAndroid::GetNativeOutputSampleRate() {
+  return Java_AudioManagerAndroid_getNativeOutputSampleRate(
+      base::android::AttachCurrentThread(),
+      j_audio_manager_.obj());
+}
+
+int AudioManagerAndroid::GetMinInputBufferSize(int rate, int channels) {
+  return Java_AudioManagerAndroid_getMinInputBufSize(
+      base::android::AttachCurrentThread(),
+      rate, channels);
+}
+
+int AudioManagerAndroid::GetMinOutputBufferSize(int rate, int channels) {
+  int min_buffer_size_bytes = Java_AudioManagerAndroid_getMinOutputBufSize(
+      base::android::AttachCurrentThread(), rate, channels);
+  // Get buffer size in frames, assuming 16-bit pcm samples.
+  return min_buffer_size_bytes / channels / 2;
+}
+
+bool AudioManagerAndroid::IsAudioLowLatencySupported() {
+  return Java_AudioManagerAndroid_isAudioLowLatencySupported(
+      base::android::AttachCurrentThread(),
+      j_audio_manager_.obj());
+}
+
+int AudioManagerAndroid::GetAudioLowLatencyFrameSize() {
+  return Java_AudioManagerAndroid_getAudioLowLatencyFrameSize(
+      base::android::AttachCurrentThread(),
+      j_audio_manager_.obj());
+}
+
 }  // namespace media