Video Compression fails

I am having an issue compressing my recorded video. I am able to begin recording with ease however, 100% of the time the compressing fails with no other errors attached. I was hoping a more experienced developer could point out any causes for issues as I have never worked with compression before.

//MARK: - Variable Declaration
@IBOutlet weak var vwPreviewLayer: UIView!

@IBOutlet weak var vwStartStopRecording: UIView!

var captureSession : AVCaptureSession?
var videoOutput : AVCaptureMovieFileOutput?
var previewLayer : AVCaptureVideoPreviewLayer?
var lpgr : UILongPressGestureRecognizer?
var captureDevice : AVCaptureDevice?
var recordDelegate : AVCaptureFileOutputRecordingDelegate?

//MARK: - View Life Cycle
override func viewDidLoad() {
    super.viewDidLoad()
    vwStartStopRecording.layer.cornerRadius = self.vwStartStopRecording.frame.size.width / 2
    vwStartStopRecording.clipsToBounds = true

    lpgr = UILongPressGestureRecognizer(target: self, action: #selector(self.action(_:)))


    lpgr!.minimumPressDuration = 0.75

    vwStartStopRecording.addGestureRecognizer(lpgr!)

    beginSession()

}

override func viewDidAppear(animated: Bool) {
    super.viewDidAppear(animated)
    previewLayer?.frame = vwPreviewLayer.bounds
}

//MARK: - BEGIN SESSION
func beginSession() {
    captureSession = AVCaptureSession()
    captureSession?.sessionPreset = AVCaptureSessionPreset1920x1080
    captureDevice = AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeVideo)

    //        let backCamera = AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeVideo)
    //        captureDevice! = backCamera!
    var input : AVCaptureDeviceInput?
    let _ : NSError?
    do {
        input = try AVCaptureDeviceInput(device: captureDevice)
    } catch let error as NSError? {
        print(error)
        return//Stop rest of code
    }
    let audioCaptureDevice = AVCaptureDevice.defaultDeviceWithMediaType(AVMediaTypeAudio)
    let audioInput : AVCaptureDeviceInput?
    let _ : NSError?
    do{
        audioInput = try AVCaptureDeviceInput(device: audioCaptureDevice)
    }
    catch let error as NSError? {
        print(error)
        return//Stop rest of code
    }

    if (captureSession?.canAddInput(audioInput))!{
        captureSession?.addInput(audioInput)
    }


    if (captureSession?.canAddInput(input))!{
        captureSession?.addInput(input)

        videoOutput = AVCaptureMovieFileOutput()
        //videoOutput?.outputSettings = [AVVideoCodecKey : AVVideoCodecKey]

        if ((captureSession?.canAddOutput(videoOutput)) != nil){
            captureSession?.addOutput(videoOutput)

            previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
            previewLayer?.videoGravity = AVLayerVideoGravityResizeAspectFill
            previewLayer?.connection.videoOrientation = AVCaptureVideoOrientation.Portrait
            vwPreviewLayer.layer.addSublayer(previewLayer!)
            captureSession?.startRunning()
        }
    }

}

//MARK: - Long Press Gesture Action
var videoData : NSData?
var url : NSURL?
var dataPath : String?
func action(gestureRecognizer:UILongPressGestureRecognizer) {
    if (lpgr!.state == UIGestureRecognizerState.Began) {
        print("Began")
        device.torchMode == AVCaptureTorchMode.On
        let paths = NSSearchPathForDirectoriesInDomains(NSSearchPathDirectory.DocumentDirectory, NSSearchPathDomainMask.UserDomainMask, true)
        let documentsDirectory: AnyObject = paths[0]
        let format = NSDateFormatter()
        format.dateFormat="yyyy-MM-dd-HH-mm-ss"
        dataPath = documentsDirectory.stringByAppendingPathComponent("/video-(format.stringFromDate(NSDate())).mp4")
        url = NSURL(fileURLWithPath: dataPath!)

        videoOutput!.startRecordingToOutputFileURL(url, recordingDelegate: self)
        print("(url)")

        NSUserDefaults.standardUserDefaults().setURL(url, forKey: "videoURL")
        NSUserDefaults.standardUserDefaults().synchronize()

    }

    if (lpgr!.state == UIGestureRecognizerState.Ended) {
        print("Ended")
        videoOutput!.stopRecording()
        device.torchMode == AVCaptureTorchMode.Off
        url = NSUserDefaults.standardUserDefaults().URLForKey("videoURL")
        let format = NSDateFormatter()
        format.dateFormat="yyyy-MM-dd-HH-mm-ss"
        let outputURl = url!.URLByDeletingLastPathComponent!.URLByAppendingPathComponent("/video(format.stringFromDate(NSDate())).mp4")
        self.compressVideo(url!, outputURL: outputURl, handler: { (session) in
            if session.status == AVAssetExportSessionStatus.Completed
                {
                    self.url! = outputURl
                    print(self.url)
                    let data = NSData(contentsOfURL: self.url!)
                    NSUserDefaults.standardUserDefaults().setURL(self.url, forKey: "videoURL")
                    NSUserDefaults.standardUserDefaults().synchronize()

                    print("File size after compression: (Double(data!.length / 1048576)) mb")
                    self.videoData = NSData(contentsOfURL: self.url!)
                    print(self.videoData)

                    self.performSegueWithIdentifier("segueTest", sender: nil)



            }

            else if session.status == AVAssetExportSessionStatus.Failed
            {
                print("failed")
            }
        })



    }
}

//MARK: - Compress Video
func compressVideo(inputURL: NSURL, outputURL: NSURL, handler:(session: AVAssetExportSession)-> Void)
{
    let urlAsset = AVURLAsset(URL: inputURL, options: nil)

    let exportSession = AVAssetExportSession(asset: urlAsset, presetName: AVAssetExportPresetMediumQuality)

    exportSession!.outputURL = outputURL

    exportSession!.outputFileType = AVFileTypeQuickTimeMovie

    exportSession!.shouldOptimizeForNetworkUse = true

    exportSession!.exportAsynchronouslyWithCompletionHandler { () -> Void in

        handler(session: exportSession!)
    }

}