gistfile1.txt

import UIKit
import AVKit
import MobileCoreServices

class ViewController: UIViewController {
    let fillImage = UIImage(named: "fill")
    let aspectImage = UIImage(named: "aspect")
    @IBOutlet weak var videoView: UIView!
    @IBOutlet weak var viewChangeButton: UIButton!

    @IBAction func onViewChange(_ sender: Any) {
        let isFill =  self.viewState == .fill
        self.viewState = isFill ? .aspect : .fill
        viewChangeButton.setImage(!isFill ? fillImage : aspectImage, for: .normal)
        self.videoLayer?.videoGravity = !isFill ? .resizeAspectFill : .resizeAspect
    }
    @IBAction func onAddVideo(_ sender: Any) {
        self.pickVideo(sourceType: UIImagePickerController.SourceType.savedPhotosAlbum)
    }
    enum ViewState {
        case fill
        case aspect
    }
    var viewState:ViewState = .fill
    let videoPicker = UIImagePickerController()
    var videoUrl:URL?
    var videoPlayer:AVPlayer?
    var videoLayer:AVPlayerLayer?

    override func viewDidLoad() {
        super.viewDidLoad()

        NotificationCenter.default.addObserver(self, selector: #selector(self.playVideoFromStart), name:NSNotification.Name.AVPlayerItemDidPlayToEndTime, object: nil)

    }
}

extension ViewController:UIImagePickerControllerDelegate, UINavigationControllerDelegate {
    func imagePickerControllerDidCancel(_ picker: UIImagePickerController) {
        dismiss(animated: true, completion: nil)
    }

    @objc func playVideoFromStart() {
        videoPlayer?.seek(to: .zero)
        videoPlayer?.play()
    }
    func removeOlderVideoLayer() {
        self.videoLayer?.removeFromSuperlayer()
    }
    func playVideo() {
        videoPlayer = AVPlayer(url: videoUrl!)
        guard let videoPlayer = self.videoPlayer else {
            return
        }

        videoPlayer.actionAtItemEnd = .none
        self.videoLayer = AVPlayerLayer(player: videoPlayer)
        guard let videoLayer = self.videoLayer else {
            return
        }
        videoLayer.frame = videoView.bounds
        videoLayer.videoGravity = self.viewState == .fill ? .resizeAspectFill : .resizeAspect
        self.videoView.layer.addSublayer(videoLayer)
        playVideoFromStart()
    }

    func pickVideo(sourceType: UIImagePickerController.SourceType) {
        guard UIImagePickerController.isSourceTypeAvailable(sourceType) else { return }
        videoPicker.sourceType = sourceType
        videoPicker.mediaTypes = [kUTTypeMovie as String]
        videoPicker.allowsEditing = false
        videoPicker.videoQuality = .typeHigh
        if #available(iOS 11.0, *) {
            videoPicker.videoExportPreset = AVAssetExportPresetPassthrough
        }
        videoPicker.delegate = self
        self.present(videoPicker, animated: true, completion: {
            self.removeOlderVideoLayer()
        })
    }

    func imagePickerController(_ picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [UIImagePickerController.InfoKey : Any]) {
        if let videoUrl = info[UIImagePickerController.InfoKey.mediaURL] as? URL {
            self.videoUrl = videoUrl
        }
        dismiss(animated: true) {
            self.playVideo()
        }
    }

}