Mute audio when volume is zero on Android.

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

Index: media/base/android/java/src/org/chromium/media/AudioManagerAndroid.java
diff --git a/media/base/android/java/src/org/chromium/media/AudioManagerAndroid.java b/media/base/android/java/src/org/chromium/media/AudioManagerAndroid.java
index db674f52d3b9f2a0a43978447f7078cdb5ef1671..93171a76975b7398ecef3e276e5b0eba9f98b5ca 100644
--- a/media/base/android/java/src/org/chromium/media/AudioManagerAndroid.java
+++ b/media/base/android/java/src/org/chromium/media/AudioManagerAndroid.java
@@ -7,16 +7,23 @@ package org.chromium.media;
 import android.bluetooth.BluetoothAdapter;
 import android.bluetooth.BluetoothManager;
 import android.content.BroadcastReceiver;
+import android.content.ContentResolver;
 import android.content.Context;
 import android.content.Intent;
 import android.content.IntentFilter;
 import android.content.pm.PackageManager;
+import android.database.ContentObserver;
 import android.media.AudioFormat;
 import android.media.AudioManager;
 import android.media.AudioRecord;
 import android.media.AudioTrack;
+import android.net.Uri;
 import android.os.Build;
+import android.os.Handler;
+import android.os.Looper;
 import android.os.Process;
+import android.provider.Settings;
+import android.provider.Settings.System;
 import android.util.Log;
 
 import java.util.Arrays;
@@ -106,6 +113,7 @@ class AudioManagerAndroid {
 
     private final AudioManager mAudioManager;
     private final Context mContext;
+    private final long mNativeAudioManagerAndroid;
 
     private boolean mHasBluetoothPermission = false;
     private boolean mIsInitialized = false;
@@ -117,18 +125,28 @@ class AudioManagerAndroid {
     // Contains a list of currently available audio devices.
     private boolean[] mAudioDevices = new boolean[DEVICE_COUNT];
 
+    private final ContentResolver mContentResolver;
+    private SettingsObserver mSettingsObserver = null;
+    private SettingsObserverThread mSettingsObserverThread = null;
+    private int mCurrentVolume;
+    private final Object mSettingsObserverLock = new Object();
+
     // Broadcast receiver for wired headset intent broadcasts.
     private BroadcastReceiver mWiredHeadsetReceiver;
 
     /** Construction */
     @CalledByNative
-    private static AudioManagerAndroid createAudioManagerAndroid(Context context) {
-        return new AudioManagerAndroid(context);
+    private static AudioManagerAndroid createAudioManagerAndroid(
+            Context context,
+            long nativeAudioManagerAndroid) {
+        return new AudioManagerAndroid(context, nativeAudioManagerAndroid);
     }
 
-    private AudioManagerAndroid(Context context) {
+    private AudioManagerAndroid(Context context, long nativeAudioManagerAndroid) {
         mContext = context;
+        mNativeAudioManagerAndroid = nativeAudioManagerAndroid;
         mAudioManager = (AudioManager)mContext.getSystemService(Context.AUDIO_SERVICE);
+        mContentResolver = mContext.getContentResolver();
     }
 
     /**
@@ -174,6 +192,16 @@ class AudioManagerAndroid {
         initBluetooth();
 
         mIsInitialized = true;
+
+        mSettingsObserverThread = new SettingsObserverThread();
+        mSettingsObserverThread.start();
+        synchronized(mSettingsObserverLock) {
+            try {
+                mSettingsObserverLock.wait();
+            } catch (InterruptedException e) {
+                Log.e(TAG, "unregisterHeadsetReceiver exception: " + e.getMessage());
+            }
+        }
     }
 
     /**
@@ -185,6 +213,14 @@ class AudioManagerAndroid {
         if (!mIsInitialized)
             return;
 
+        if (mSettingsObserverThread != null ) {
+            mSettingsObserverThread = null;
+        }
+        if (mSettingsObserver != null) {
+            mContentResolver.unregisterContentObserver(mSettingsObserver);
+            mSettingsObserver = null;
+        }
+
         unregisterForWiredHeadsetIntentBroadcast();
 
         // Restore previously stored audio states.
@@ -553,4 +589,40 @@ class AudioManagerAndroid {
     private void loge(String msg) {
         Log.e(TAG, msg);
     }
+
+    private class SettingsObserver extends ContentObserver {
+        SettingsObserver() {
+            super(new Handler());
+            mContentResolver.registerContentObserver(Settings.System.CONTENT_URI, true, this);

[jmtrivi, 2013/12/02 23:57:59]

Be aware that this will be called for many more things than volume changes. I
know there isn't any public mechanism to monitor volume changes.

[wjia(left Chromium), 2013/12/03 23:08:06]

Thanks for the reminder! Yes, I am aware of this. Once a public mechanism is
available (if it will be), we will switch to listening to volume specific
changes.

+        }
+
+        @Override
+        public void onChange(boolean selfChange) {

[jmtrivi, 2013/12/02 23:57:59]

This will only work for volume changes when the audio configuration remains the
same: as volume is device-dependent, when you switch the audio device (e.g. user
unplugs headset), your settings observer will not be called.

[wjia(left Chromium), 2013/12/03 23:08:06]

Right, switching audio device is a problem (I have mentioned it in an email
thread). I have tried to call mAudioManager.getStreamVolume() when device is
changed in BroadcastReceiver::onReceive() defined above (line 415). But somehow
the AudioManager doesn't give me inconsistent result. For example,
1. put earpiece volume at 0;
2. plug headset, query volume of STREAM_VOICE_CALL in onReceive(), it's 0;
3. change headset volume to 5;
4. unplug headset, query volume of STREAM_VOICE_CALL in onReceive(), it's 4 (I
expect it's 5 at least, but it's 4).

If I modify the step #3 to change the volume to 3, unplug headset, now
AudioManager gives me volume of 3 or 0.

Basically, AudioManager.getStreamVolume() could return 3 different results when
called inside BroadcastReceiver::onReceive():
a. the previous volume of the new device;
b. the volume of previous device;
c. 4 (which I have no clue why it's 4);

I am not sure if that's a bug, or I use it in a wrong way (e.g., on when/how to
query AudioManager for stream volume, etc). I hope you can shed some light on
it.

+            super.onChange(selfChange);
+            int volume = mAudioManager.getStreamVolume(AudioManager.STREAM_VOICE_CALL);
+            nativeSetMute(mNativeAudioManagerAndroid, (volume == 0));

[jmtrivi, 2013/12/02 23:57:59]

You should post a message to do this asynchronously to better handle the case of
multiple volume changes (as is the case when the user bring the volume down
quickly to 0). You could also maintain state so you only update the native layer
on a state change.

[wjia(left Chromium), 2013/12/03 23:08:06]

The message posting happens in c++ code, i.e., AudioManagerAndroid::SetMute(). 

I have tried maintaining a state here to avoid unnecessary function call to c++
code. But I gave it up because it messed up the case when device is changed.

+        }
+    }
+
+    private native void nativeSetMute(long nativeAudioManagerAndroid, boolean muted);
+
+    private class SettingsObserverThread extends Thread {
+        SettingsObserverThread() {
+            super("SettinsObserver");
+        }
+
+        @Override
+        public void run() {
+            // Set this thread up so the handler will work on it.
+            Looper.prepare();
+
+            synchronized(mSettingsObserverLock) {
+                mSettingsObserver = new SettingsObserver();
+                mSettingsObserverLock.notify();
+            }
+
+            // Listen for volume change.
+            Looper.loop();
+        }
+    }
 }