原理：开启红外感应，根据红外感应气话播放听筒还是扬声器。

[[UIDevice currentDevice] setProximityMonitoringEnabled:YES]; //建议在播放之前设置yes，播放结束设置NO，这个功能是开启红外感应//添加监听[[NSNotificationCenter defaultCenter] addObserver:selfselector:@selector(sensorStateChange:)name:@"UIDeviceProximityStateDidChangeNotification"object:nil];//处理监听触发事件-(void)sensorStateChange:(NSNotificationCenter *)notification;{//如果此时手机靠近面部放在耳朵旁，那么声音将通过听筒输出，并将屏幕变暗（省电啊）if ([[UIDevice currentDevice] proximityState] == YES){NSLog(@"Device is close to user");[[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayAndRecord error:nil];}else{NSLog(@"Device is not close to user");[[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryPlayback error:nil];}}//初始化播放器的时候如下设置UInt32 sessionCategory = kAudioSessionCategory_MediaPlayback;AudioSessionSetProperty(kAudioSessionProperty_AudioCategory,sizeof(sessionCategory),&sessionCategory); UInt32 audioRouteOverride = kAudioSessionOverrideAudioRoute_Speaker;AudioSessionSetProperty (kAudioSessionProperty_OverrideAudioRoute,sizeof (audioRouteOverride),&audioRouteOverride);AVAudioSession *audioSession = [AVAudioSession sharedInstance];//默认情况下扬声器播放[audioSession setCategory:AVAudioSessionCategoryPlayback error:nil];[audioSession setActive:YES error:nil];