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

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

 // Copyright 2013 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.
 
 package org.chromium.media;
 
 import android.content.BroadcastReceiver;
 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;
 
 import org.chromium.base.CalledByNative;
 import org.chromium.base.JNINamespace;
 
 @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;
+    private static final int DEFAULT_FRAME_PER_BUFFER = 256;

[no longer working on chromium, 2013/05/20 09:59:26]

why 256 is the default one?
Add comment please.

[leozwang1, 2013/05/20 17:41:05]

Done.

 
     private final AudioManager mAudioManager;
     private final Context mContext;
 
     private BroadcastReceiver mReceiver;
     private boolean mOriginalSpeakerStatus;
 
     @CalledByNative
     public void setMode(int mode) {
         try {
@@ skipping 40 matching lines @@
         mContext.registerReceiver(mReceiver, filter);
     }
 
     @CalledByNative
     public void unregisterHeadsetReceiver() {
         mContext.unregisterReceiver(mReceiver);
         mReceiver = null;
         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);
             return (sampleRateString == null ?
                     DEFAULT_SAMPLING_RATE : Integer.parseInt(sampleRateString));
         } else {
             return DEFAULT_SAMPLING_RATE;
         }
     }
 
-    private void logDeviceInfo() {
-        Log.i(TAG, "Manufacturer:" + Build.MANUFACTURER +
-                  " Board: " + Build.BOARD + " Device: " + Build.DEVICE +
-                  " Model: " + Build.MODEL + " PRODUCT: " + Build.PRODUCT);
+    @CalledByNative
+    private static int getMinInputBufSize(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);
     }
+
+    @CalledByNative
+    private static int getMinOutputBufSize(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);
+    }
+
+    @CalledByNative
+    private boolean isAudioLowLatencySupported() {
+        return mContext.getPackageManager().hasSystemFeature(
+                PackageManager.FEATURE_AUDIO_LOW_LATENCY);
+    }
+
+    @CalledByNative
+    private int getAudioLowLatencyFrameSize() {
+        String framesPerBuffer =
+                mAudioManager.getProperty(AudioManager.PROPERTY_OUTPUT_FRAMES_PER_BUFFER);
+        return (framesPerBuffer == null ?
+                DEFAULT_FRAME_PER_BUFFER : Integer.parseInt(framesPerBuffer));
+    }
+
 }