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 200599)
+++ media/audio/android/audio_manager_android.cc	(working copy)
@@ -22,6 +22,9 @@
 static const int kAudioModeNormal = 0x00000000;
 static const int kAudioModeInCommunication = 0x00000003;
 
+static const int kDefaultInputBufferSize = 1024;
+static const int kDefaultOutputBufferSize = 2048;
+
 AudioManager* CreateAudioManager() {
   return new AudioManagerAndroid();
 }
@@ -56,13 +59,11 @@
 
 AudioParameters AudioManagerAndroid::GetInputStreamParameters(
     const std::string& device_id) {
-  // TODO(leozwang): Android defines the minimal buffer size requirment
-  // we should use it.
-  static const int kDefaultBufferSize = 1024;
-  // TODO(xians): query the native channel layout for the specific device.
+  int buffer_size = GetMinInputFrameSize(GetNativeOutputSampleRate(), 2);
   return AudioParameters(
       AudioParameters::AUDIO_PCM_LOW_LATENCY, CHANNEL_LAYOUT_STEREO,
-      GetNativeOutputSampleRate(), 16, kDefaultBufferSize);
+      GetNativeOutputSampleRate(), 16,
+      buffer_size <= 0 ? kDefaultInputBufferSize : buffer_size);
 }
 
 AudioOutputStream* AudioManagerAndroid::MakeAudioOutputStream(
@@ -119,15 +120,25 @@
   return new OpenSLESInputStream(this, params);
 }
 
+int AudioManagerAndroid::GetOptimalOutputFrameSize(int sample_rate,
+                                                        int channels) {

[no longer working on chromium, 2013/05/21 21:52:33]

indentation.

+  if (IsAudioLowLatencySupported()) {
+    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 ((kDefaultOutputBufferSize + frame_size / 2) / frame_size) *
+      frame_size;
+  } else {
+    return std::max(kDefaultOutputBufferSize,
+                    GetMinOutputFrameSize(sample_rate, channels));

[no longer working on chromium, 2013/05/21 21:52:33]

why the output code is different from the way of input buffer size?
shouldn't it be:
int buffer_size = GetMinOutputFrameSize(sample_rate, channels);
return buffer_size > 0 ? buffer_size : kDefaultOutputBufferSize

[leozwang1, 2013/05/22 06:33:19]

The return value of GetMinOutputFrameSize is small on some android devices, we
take max of these two variables.

+  }
+}
+
 AudioParameters AudioManagerAndroid::GetPreferredOutputStreamParameters(
     const AudioParameters& input_params) {
-  // TODO(leozwang): Android defines the minimal buffer size requirment
-  // we should use it.
-  static const int kDefaultBufferSize = 2048;
-
   ChannelLayout channel_layout = CHANNEL_LAYOUT_STEREO;
   int sample_rate = GetNativeOutputSampleRate();
-  int buffer_size = kDefaultBufferSize;
+  int buffer_size = GetOptimalOutputFrameSize(sample_rate, 2);

[no longer working on chromium, 2013/05/21 21:52:33]

This is not correct. In case input_params.IsValid() below, we will open the
device with input_params.channel_layout(), it might be mono or stereo.
Move the code below, and get the buffer size based on the correct channel
layout.

[leozwang1, 2013/05/22 06:33:19]

I was puzzled by the original logic, from what you said, if
input_params.IsValid(), the code always use kDefaultBufferSize regardless
channel_layout(), is it correct? Just want to make sure I understand the problem
before I upload a patch.

[no longer working on chromium, 2013/05/22 21:00:00]

The value we are setting here is frames_per_buffer, which can be interpreted as
the numbers of samples per channel when getting a packet.
You can check the details in audio_parameters.h

To answer your question more explicitly, previously we are using
kDefaultBufferSize as the buffer size for 1 channel. If it is in stereo mode,
the total buffer size will be 2*kDefaultBufferSize

   int bits_per_sample = 16;
   int input_channels = 0;
   if (input_params.IsValid()) {
@@ -136,8 +147,6 @@
     bits_per_sample = input_params.bits_per_sample();
     channel_layout = input_params.channel_layout();
     input_channels = input_params.input_channels();
-
-    buffer_size = std::min(buffer_size, input_params.frames_per_buffer());
   }
 
   int user_buffer_size = GetUserBufferSize();
@@ -178,4 +187,31 @@
       j_audio_manager_.obj());
 }
 
+int AudioManagerAndroid::GetMinInputFrameSize(int rate, int channels) {
+  // Java_AudioManagerAndroid_getMinInputBufSize return buffer size in bytes,
+  // convert it to size in frame.
+  return Java_AudioManagerAndroid_getMinInputBufSize(
+      base::android::AttachCurrentThread(), rate, channels) /
+      sizeof(int16) / channels;
+}
+
+int AudioManagerAndroid::GetMinOutputFrameSize(int rate, int channels) {
+  // Get buffer size in frames, assuming 16-bit pcm samples.
+  return Java_AudioManagerAndroid_getMinOutputBufSize(
+      base::android::AttachCurrentThread(), rate, channels) /
+      sizeof(int16) / channels;
+}
+
+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