ARKitで画像のトラッキングが外れた際に動画を一時停止したい。

解決したいこと

ARKitを使用し、トラッキングした画像の上に動画を再生します。
画像からトラッキングが外れた時でも動画が再生され続け、音も流れっぱなしなので一時停止したいです。

やったこと

下記コードにより、トラッキングが外れた際に動画の一時停止を実現しようと試みました。
しかし、画像をトラッキングした瞬間にアプリが落ちてしまいます。
原因がわかりません。

swift
1    func session(_ session: ARSession, didUpdate frame: ARFrame) {
2        if !sceneView.isNode(videoHolder!, insideFrustumOf: sceneView!.pointOfView!) {
3            videoPlayerNode?.pause()
4        }
5    }

全体のコード

swift
1import UIKit
2import SceneKit
3import ARKit
4import SafariServices
5import AVFoundation
6
7class ViewController: UIViewController, ARSCNViewDelegate, ARSessionDelegate {
8    @IBOutlet var sceneView: ARSCNView!
9    
10    let referenceImages = ARReferenceImage.referenceImages(inGroupNamed: "AR Resources", bundle: Bundle.main)
11    
12   
13    override func viewDidLoad() {
14        super.viewDidLoad()
15        
16        let scene = SCNScene()
17        sceneView.scene = scene
18    }
19    
20    
21    override func viewWillAppear(_ animated: Bool) {
22        super.viewWillAppear(animated)
23        
24        let configuration = ARImageTrackingConfiguration()
25        
26        configuration.trackingImages = referenceImages!
27        
28        sceneView.session.run(configuration)
29
30    }
31    
32    var videoHolder: SCNNode?
33
34    
35    func renderer(_ renderer: SCNSceneRenderer, didAdd node: SCNNode, for anchor: ARAnchor) {
36
37        guard let imageAnchor = anchor as? ARImageAnchor else { return }
38        
39        let referenceImage = imageAnchor.referenceImage
40        
41        let width = CGFloat(referenceImage.physicalSize.width)
42        let height = CGFloat(referenceImage.physicalSize.height)
43        
44        let videoHolderGeometry = SCNPlane(width: width, height: height)
45
46        videoHolder!.transform = SCNMatrix4MakeRotation(-Float.pi / 2, 1, 0, 0)
47
48        videoHolder!.geometry = videoHolderGeometry
49        
50        if let videoURL = Bundle.main.url(forResource: "img.scnassets/route", withExtension: "MOV"){
51            setupVideoOnNode(videoHolder!, fromURL: videoURL)
52        }
53        
54
55        node.addChildNode(videoHolder!)
56        
57        videoHolder!.name = "route"
58    }
59    
60    
61    var videoPlayerNode: SKVideoNode?
62    var videoPlayer: AVPlayer?
63    
64
65    func setupVideoOnNode(_ node: SCNNode, fromURL url: URL){
66
67        let videoPlayer = AVPlayer(url: url)
68
69        videoPlayerNode = SKVideoNode(avPlayer: videoPlayer)
70        videoPlayerNode?.yScale = -1
71        
72
73        let spriteKitScene = SKScene(size: CGSize(width: 1000, height: 1000))
74        spriteKitScene.scaleMode = .aspectFit
75        videoPlayerNode?.position = CGPoint(x: spriteKitScene.size.width/2, y: spriteKitScene.size.height/2)
76        videoPlayerNode?.size = spriteKitScene.size
77        spriteKitScene.addChild(videoPlayerNode!)
78        
79
80        node.geometry?.firstMaterial?.diffuse.contents = spriteKitScene
81        
82
83        videoPlayerNode?.play()
84        videoPlayer.volume = 100
85        
86        //ループ再生
87        videoPlayer.actionAtItemEnd = AVPlayer.ActionAtItemEnd.none;
88        NotificationCenter.default.addObserver(self,
89                                               selector: #selector(self.stateEnd),
90                                               name: NSNotification.Name("AVPlayerItemDidPlayToEndTimeNotification"),
91                                               object: videoPlayer.currentItem)
92        
93    }
94    
95    
96    @objc func stateEnd(notification: NSNotification) {
97        let avPlayerItem = notification.object as? AVPlayerItem
98        avPlayerItem?.seek(to: CMTime.zero)
99    }
100    
101    
102    func session(_ session: ARSession, didUpdate frame: ARFrame) {
103        if !sceneView.isNode(videoHolder!, insideFrustumOf: sceneView!.pointOfView!) {
104            videoPlayerNode?.pause()
105        }
106    }
107    
108    // 画面に表示された直後に呼ばれる。
109    override func viewWillDisappear(_ animated: Bool) {
110        super.viewWillDisappear(animated)
111        sceneView.session.pause()
112    }
113
114    
115    
116    override func touchesBegan(_ touches: Set<UITouch>, with event: UIEvent?) {
117        guard let location = touches.first?.location(in: sceneView),
118            let result = sceneView.hitTest(location, options: nil).first else {
119                return
120        }
121        let node = result.node
122        
123        if node.name == "route" {
124            let safariVC = SFSafariViewController(url: URL(string: "https://images.google.com/?gws_rd=ssl")!)
125            self.present(safariVC, animated: true, completion: nil)
126        }
127    }
128    
129    
130}
131