Use RTCAudioSessionDelegate in AudioDeviceIOS.

webrtc/modules/audio_device/ios/objc/RTCAudioSession+Configuration.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 31 matching lines @@
 
   if (self.mode != configuration.mode) {
     NSError *modeError = nil;
     if (![self setMode:configuration.mode error:&modeError]) {
       RTCLogError(@"Failed to set mode: %@",
                   modeError.localizedDescription);
       error = modeError;
     }
   }
 
-  if (self.sampleRate != configuration.sampleRate) {
+  // self.sampleRate is accurate only if the audio session is active.
+  if (!self.isActive || self.sampleRate != configuration.sampleRate) {
     NSError *sampleRateError = nil;
     if (![self setPreferredSampleRate:configuration.sampleRate
                                 error:&sampleRateError]) {
       RTCLogError(@"Failed to set preferred sample rate: %@",
                   sampleRateError.localizedDescription);
       error = sampleRateError;
     }
   }
 
-  if (self.IOBufferDuration != configuration.ioBufferDuration) {
+  // self.IOBufferDuration is accurate only if the audio session is active.
+  if (!self.isActive ||
+      self.IOBufferDuration != configuration.ioBufferDuration) {
     NSError *bufferDurationError = nil;
     if (![self setPreferredIOBufferDuration:configuration.ioBufferDuration
                                       error:&bufferDurationError]) {
       RTCLogError(@"Failed to set preferred IO buffer duration: %@",
                   bufferDurationError.localizedDescription);
       error = bufferDurationError;
     }
   }
 
   NSError *activeError = nil;
@@ skipping 103 matching lines @@
     RTCLog(@"Current mode %@ does not match %@",
            currentConfig.mode,
            webRTCConfig.mode);
     return NO;
   }
 
   return YES;
 }
 
 @end