Swift capture video to different paths - swift

Question

I'm trying to capture a video using swift. I want to capture the video in a new file every x seconds.
Here is my current code:
var i = 0
override func viewDidLoad() {
super.viewDidLoad()
if setupSession() {
setupPreview()
startSession()
}
}
func setupSession() -> Bool {
...
return true
}
func startSession() {
...
}
func tempURL() -> URL? {
let directory = NSTemporaryDirectory() as NSString
if directory != "" {
i = i+1
old_cur_videoID = cur_videoID_system
cur_videoID_system = "\(cur_videoID)_\(i).mp4"
let path = directory.appendingPathComponent(cur_videoID_system)
return URL(fileURLWithPath: path)
}
return nil
}
func startRecording() {
let delayTime = DispatchTime.now() + 2
DispatchQueue.main.asyncAfter(deadline: delayTime) {
self.startRecording()
}
outputURL = tempURL()
movieOutput.startRecording(toOutputFileURL: outputURL, recordingDelegate: self)
}
And the two delegate functions:
func capture(_ captureOutput: AVCaptureFileOutput!, didStartRecordingToOutputFileAt fileURL: URL!, fromConnections connections: [Any]!) {
}
func capture(_ captureOutput: AVCaptureFileOutput!, didFinishRecordingToOutputFileAt outputFileURL: URL!, fromConnections connections: [Any]!, error: Error!) {
if (error != nil) {
print("Error recording movie: \(error!.localizedDescription)")
} else {
if(i > 1){
saveOnServer()
}
}
outputURL = nil
}
If I try to run the Code, I get the following Error-Message:
Error recording movie: Movie recording cannot be started
Can somebody help me with my problem? If more code is necessary or some parts are unclear, please feel free to ask.
Thanks a lot!