AVCaptureMovieFileOutput - 没有活动启用的连接

在使用iOS开发中，有时我们需要使用摄像头来录制视频。AVCaptureMovieFileOutput是一个用于录制视频的类，它可以将摄像头的输出写入一个文件中。然而，在使用AVCaptureMovieFileOutput时，我们可能会遇到一个常见的问题，即"没有活动/启用的连接"的错误。

swift
import AVFoundation
class ViewController: UIViewController {
    var captureSession: AVCaptureSession!
    var movieOutput: AVCaptureMovieFileOutput!
    var videoPreviewLayer: AVCaptureVideoPreviewLayer!
    override func viewDidLoad() {
        super.viewDidLoad()
        
        // 创建捕捉会话
        captureSession = AVCaptureSession()
        
        // 设置摄像头
        guard let videoDevice = AVCaptureDevice.default(for: .video) else { return }
        guard let videoInput = try? AVCaptureDeviceInput(device: videoDevice) else { return }
        
        // 添加输入设备到会话
        if captureSession.canAddInput(videoInput) {
            captureSession.addInput(videoInput)
        }
        
        // 设置输出
        movieOutput = AVCaptureMovieFileOutput()
        
        // 添加输出设备到会话
        if captureSession.canAddOutput(movieOutput) {
            captureSession.addOutput(movieOutput)
        }
        
        // 设置预览层
        videoPreviewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
        videoPreviewLayer.videoGravity = .resizeAspectFill
        videoPreviewLayer.frame = view.bounds
        view.layer.addSublayer(videoPreviewLayer)
        
        // 启动会话
        captureSession.startRunning()
    }
    
    // 开始录制视频
    func startRecording() {
        let outputURL = URL(fileURLWithPath: NSTemporaryDirectory()).appendingPathComponent("video.mov")
        movieOutput.startRecording(to: outputURL, recordingDelegate: self)
    }
    
    // 停止录制视频
    func stopRecording() {
        movieOutput.stopRecording()
    }
}
extension ViewController: AVCaptureFileOutputRecordingDelegate {
    // 录制完成
    func fileOutput(_ output: AVCaptureFileOutput, didFinishRecordingTo outputFileURL: URL, from connections: [AVCaptureConnection], error: Error?) {
        if let error = error {
            print("录制视频出错：\(error.localizedDescription)")
        } else {
            print("视频录制完成：\(outputFileURL.absoluteString)")
        }
    }
}