Use RTCAudioSessionDelegate in AudioDeviceIOS.

webrtc/modules/audio_device/ios/objc/RTCAudioSessionDelegateAdapter.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.
+ */
+
+#import "webrtc/modules/audio_device/ios/objc/RTCAudioSessionDelegateAdapter.h"
+
+#include "webrtc/modules/audio_device/ios/audio_session_observer.h"
+
+#import "webrtc/base/objc/RTCLogging.h"
+
+@implementation RTCAudioSessionDelegateAdapter {
+  webrtc::AudioSessionObserver *_observer;
+}
+
+- (instancetype)initWithObserver:(webrtc::AudioSessionObserver *)observer {
+  NSParameterAssert(observer);
+  if (self = [super init]) {
+    _observer = observer;
+  }
+  return self;
+}
+
+#pragma mark - RTCAudioSessionDelegate
+
+- (void)audioSessionDidBeginInterruption:(RTCAudioSession *)session {
+  _observer->OnInterruptionBegin();
+}
+
+- (void)audioSessionDidEndInterruption:(RTCAudioSession *)session
+                   shouldResumeSession:(BOOL)shouldResumeSession {
+  _observer->OnInterruptionEnd();
+}
+
+- (void)audioSessionDidChangeRoute:(RTCAudioSession *)session
+           reason:(AVAudioSessionRouteChangeReason)reason
+    previousRoute:(AVAudioSessionRouteDescription *)previousRoute {
+  switch (reason) {
+    case AVAudioSessionRouteChangeReasonUnknown:
+    case AVAudioSessionRouteChangeReasonNewDeviceAvailable:
+    case AVAudioSessionRouteChangeReasonOldDeviceUnavailable:
+    case AVAudioSessionRouteChangeReasonCategoryChange:
+      // It turns out that we see a category change (at least in iOS 9.2)
+      // when making a switch from a BT device to e.g. Speaker using the
+      // iOS Control Center and that we therefore must check if the sample
+      // rate has changed. And if so is the case, restart the audio unit.
+    case AVAudioSessionRouteChangeReasonOverride:
+    case AVAudioSessionRouteChangeReasonWakeFromSleep:
+    case AVAudioSessionRouteChangeReasonNoSuitableRouteForCategory:
+      _observer->OnValidRouteChange();
+      break;
+    case AVAudioSessionRouteChangeReasonRouteConfigurationChange:
+      // The set of input and output ports has not changed, but their
+      // configuration has, e.g., a port’s selected data source has
+      // changed. Ignore this type of route change since we are focusing
+      // on detecting headset changes.
+      RTCLog(@"Ignoring RouteConfigurationChange");
+      break;
+  }
+}
+
+- (void)audioSessionMediaServicesWereLost:(RTCAudioSession *)session {
+}
+
+- (void)audioSessionMediaServicesWereReset:(RTCAudioSession *)session {
+}
+
+- (void)audioSessionShouldConfigure:(RTCAudioSession *)session {
+}
+
+- (void)audioSessionShouldUnconfigure:(RTCAudioSession *)session {
+}
+
+@end