解决iOS程序耳机有声音，外放没声音的问题

在AppDelegeate中添加如下代码：

func application(application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]?) -> Bool {
// Override point for customization after application launch.
AppDelegate.instance = self

let session = AVAudioSession.sharedInstance()
do{
try session.setCategory(AVAudioSessionCategoryPlayAndRecord, withOptions: AVAudioSessionCategoryOptions.MixWithOthers)
} catch let err as NSError {
NSLog(err.description)
}

return true
}