Adds support for AVAudioSessionSilenceSecondaryAudioHintNotification on iOS

webrtc/modules/audio_device/ios/objc/RTCAudioSession.mm

 /*
  *  Copyright 2016 The WebRTC Project Authors. All rights reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
@@ skipping 48 matching lines @@
 
     NSNotificationCenter *center = [NSNotificationCenter defaultCenter];
     [center addObserver:self
                selector:@selector(handleInterruptionNotification:)
                    name:AVAudioSessionInterruptionNotification
                  object:nil];
     [center addObserver:self
                selector:@selector(handleRouteChangeNotification:)
                    name:AVAudioSessionRouteChangeNotification
                  object:nil];
-    // TODO(tkchin): Maybe listen to SilenceSecondaryAudioHintNotification.
     [center addObserver:self
                selector:@selector(handleMediaServicesWereLost:)
                    name:AVAudioSessionMediaServicesWereLostNotification
                  object:nil];
     [center addObserver:self
                selector:@selector(handleMediaServicesWereReset:)
                    name:AVAudioSessionMediaServicesWereResetNotification
                  object:nil];
+    // Posted on the main thread when the primary audio from other applications
+    // starts and stops. Foreground applications may use this notification as a
+    // hint to enable or disable audio that is secondary.
+    [center addObserver:self
+               selector:@selector(handleSilenceSecondaryAudioHintNotification:)
+                   name:AVAudioSessionSilenceSecondaryAudioHintNotification
+                 object:nil];
     // Also track foreground event in order to deal with interruption ended situation.
     [center addObserver:self
                selector:@selector(handleApplicationDidBecomeActive:)
                    name:UIApplicationDidBecomeActiveNotification
                  object:nil];
   }
   return self;
 }
 
 - (void)dealloc {
@@ skipping 421 matching lines @@
   [self updateAudioSessionAfterEvent];
   [self notifyMediaServicesWereLost];
 }
 
 - (void)handleMediaServicesWereReset:(NSNotification *)notification {
   RTCLog(@"Media services were reset.");
   [self updateAudioSessionAfterEvent];
   [self notifyMediaServicesWereReset];
 }
 
+- (void)handleSilenceSecondaryAudioHintNotification:(NSNotification *)notification {
+  // TODO(henrika): just adding logs here for now until we know if we are ever
+  // see this notification and might be affected by it or if further actions
+  // are required.
+  NSNumber *typeNumber =
+      notification.userInfo[AVAudioSessionSilenceSecondaryAudioHintTypeKey];
+  AVAudioSessionSilenceSecondaryAudioHintType type =
+      (AVAudioSessionSilenceSecondaryAudioHintType)typeNumber.unsignedIntegerValue;
+  switch (type) {
+    case AVAudioSessionSilenceSecondaryAudioHintTypeBegin:
+      RTCLog(@"Another application's primary audio has started.");
+      break;
+    case AVAudioSessionSilenceSecondaryAudioHintTypeEnd:
+      RTCLog(@"Another application's primary audio has stopped.");
+      break;
+  }
+}
+
 - (void)handleApplicationDidBecomeActive:(NSNotification *)notification {
   if (self.isInterrupted) {
     RTCLog(@"Application became active after an interruption. Treating as interruption end.");
     self.isInterrupted = NO;
     [self updateAudioSessionAfterEvent];
     [self notifyDidEndInterruptionWithShouldResumeSession:YES];
   }
 }
 
 #pragma mark - Private
@@ skipping 294 matching lines @@
 - (void)notifyDidStopPlayOrRecord {
   for (auto delegate : self.delegates) {
     SEL sel = @selector(audioSessionDidStopPlayOrRecord:);
     if ([delegate respondsToSelector:sel]) {
       [delegate audioSessionDidStopPlayOrRecord:self];
     }
   }
 }
 
 @end