IOS swift 录音报错找不到原因

var recordSetting=NSMutableDictionary()//录音设置
//设置录音格式 AVFormatIDKey==kAudioFormatLinearPCM
recordSetting.setValue(kAudioFormatMPEG4AAC, forKey: AVFormatIDKey)
//设置录音采样率(Hz) 如：AVSampleRateKey==8000/44100/96000（影响音频的质量）
recordSetting.setValue(44100, forKey: AVSampleRateKey)
//录音通道数 1 或 2
recordSetting.setValue(1, forKey: AVNumberOfChannelsKey)
//线性采样位数 8、16、24、32
recordSetting.setValue(16, forKey:AVLinearPCMBitDepthKey)
//录音的质量
recordSetting.setValue(AVAudioQuality.High.hashValue, forKey: AVEncoderAudioQualityKey)

    self.session = AVAudioSession.sharedInstance()
    self.session.setCategory(AVAudioSessionCategoryPlayAndRecord, error: nil)
    session.setActive(true, error: nil)

    //开启音量检测
    var strUrl=NSSearchPathForDirectoriesInDomains(NSSearchPathDirectory.DocumentDirectory, NSSearchPathDomainMask.UserDomainMask, true)[0] as! NSString
    var pathComponents = [strUrl,"sound.m4a"]
    var url = NSURL.fileURLWithPathComponents(pathC![图片说明](https://img-ask.csdn.net/upload/201508/11/1439296049_555623.png)omponents)!
    urlPlay=url
    recorder = AVAudioRecorder(URL: url, settings: recordSetting as [NSObject : AnyObject], error: nil)!      **这句话报错，错误原因如图？该怎么改呢，为什么是这个原因呢**？
    //开启音量检测
    recorder.meteringEnabled=true
    recorder.prepareToRecord()

http://download.csdn.net/download/u011222418/6552025

http://plter.lofter.com/post/c6445_1a47d2d