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

media/base/android/java/src/org/chromium/media/AudioManagerAndroid.java

Index: media/base/android/java/src/org/chromium/media/AudioManagerAndroid.java
===================================================================
--- media/base/android/java/src/org/chromium/media/AudioManagerAndroid.java	(revision 201553)
+++ media/base/android/java/src/org/chromium/media/AudioManagerAndroid.java	(working copy)
@@ -8,7 +8,11 @@
 import android.content.Context;
 import android.content.Intent;
 import android.content.IntentFilter;
+import android.content.pm.PackageManager;
+import android.media.AudioFormat;
 import android.media.AudioManager;
+import android.media.AudioRecord;
+import android.media.AudioTrack;
 import android.os.Build;
 import android.util.Log;
 
@@ -18,9 +22,14 @@
 @JNINamespace("media")
 class AudioManagerAndroid {
     private static final String TAG = AudioManagerAndroid.class.getSimpleName();
+
     // Most of Google lead devices use 44.1K as the default sampling rate, 44.1K
     // is also widely used on other android devices.
     private static final int DEFAULT_SAMPLING_RATE = 44100;
+    // Randomly picked up frame size which is close to return value on N4.
+    // Return this default value when
+    // getProperty(PROPERTY_OUTPUT_FRAMES_PER_BUFFER) fails.
+    private static final int DEFAULT_FRAME_PER_BUFFER = 256;
 
     private final AudioManager mAudioManager;
     private final Context mContext;
@@ -81,8 +90,14 @@
         mAudioManager.setSpeakerphoneOn(mOriginalSpeakerStatus);
     }
 
+    private void logDeviceInfo() {
+        Log.i(TAG, "Manufacturer:" + Build.MANUFACTURER +
+                " Board: " + Build.BOARD + " Device: " + Build.DEVICE +
+                " Model: " + Build.MODEL + " PRODUCT: " + Build.PRODUCT);
+    }
+
     @CalledByNative
-    public int getNativeOutputSampleRate() {
+    private int getNativeOutputSampleRate() {
         if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.JELLY_BEAN_MR1) {
             String sampleRateString = mAudioManager.getProperty(
                     AudioManager.PROPERTY_OUTPUT_SAMPLE_RATE);
@@ -93,9 +108,58 @@
         }
     }
 
-    private void logDeviceInfo() {
-        Log.i(TAG, "Manufacturer:" + Build.MANUFACTURER +
-                  " Board: " + Build.BOARD + " Device: " + Build.DEVICE +
-                  " Model: " + Build.MODEL + " PRODUCT: " + Build.PRODUCT);
+  /**
+   * Returns the minimum frame size required for audio input.
+   *
+   * @param sampleRate sampling rate
+   * @param channels number of channels
+   */
+    @CalledByNative
+    private static int getMinInputFrameSize(int sampleRate, int channels) {
+        int channelConfig;
+        if (channels == 1) {
+            channelConfig = AudioFormat.CHANNEL_IN_MONO;
+        } else if (channels == 2) {
+            channelConfig = AudioFormat.CHANNEL_IN_STEREO;
+        } else {
+            return -1;
+        }
+        return AudioRecord.getMinBufferSize(
+                sampleRate, channelConfig, AudioFormat.ENCODING_PCM_16BIT) / 2 / channels;
     }
+
+  /**
+   * Returns the minimum frame size required for audio output.
+   *
+   * @param sampleRate sampling rate
+   * @param channels number of channels
+   */
+    @CalledByNative
+    private static int getMinOutputFrameSize(int sampleRate, int channels) {
+        int channelConfig;
+        if (channels == 1) {
+            channelConfig = AudioFormat.CHANNEL_OUT_MONO;
+        } else if (channels == 2) {
+            channelConfig = AudioFormat.CHANNEL_OUT_STEREO;
+        } else {
+            return -1;
+        }
+        return AudioTrack.getMinBufferSize(
+                sampleRate, channelConfig, AudioFormat.ENCODING_PCM_16BIT) / 2 / channels;
+    }
+
+    @CalledByNative
+    private boolean isAudioLowLatencySupported() {
+        return mContext.getPackageManager().hasSystemFeature(
+                PackageManager.FEATURE_AUDIO_LOW_LATENCY);
+    }
+
+    @CalledByNative
+    private int getAudioLowLatencyOutputFrameSize() {
+        String framesPerBuffer =
+                mAudioManager.getProperty(AudioManager.PROPERTY_OUTPUT_FRAMES_PER_BUFFER);
+        return (framesPerBuffer == null ?
+                DEFAULT_FRAME_PER_BUFFER : Integer.parseInt(framesPerBuffer));
+    }
+
 }