要实现AR会话和录制视频的功能，可以使用ARKit和AVFoundation框架来完成。下面是一个示例代码，演示了如何创建AR会话并录制视频：

import ARKit
import AVFoundation

class ViewController: UIViewController, ARSessionDelegate {

    var arSession: ARSession!
    var recorder: AVAssetWriter!
    var videoInput: AVAssetWriterInput!
    var pixelBufferAdaptor: AVAssetWriterInputPixelBufferAdaptor!
    var isRecording = false

    override func viewDidLoad() {
        super.viewDidLoad()

        // 设置AR会话
        arSession = ARSession()
        arSession.delegate = self

        // 创建视频录制器
        let videoOutputSettings = [
            AVVideoCodecKey: AVVideoCodecType.h264,
            AVVideoWidthKey: UIScreen.main.bounds.width,
            AVVideoHeightKey: UIScreen.main.bounds.height
        ] as [String : Any]
        videoInput = AVAssetWriterInput(mediaType: .video, outputSettings: videoOutputSettings)
        let pixelBufferAttributes = [
            kCVPixelBufferPixelFormatTypeKey as String: kCVPixelFormatType_32ARGB,
            kCVPixelBufferWidthKey as String: UIScreen.main.bounds.width,
            kCVPixelBufferHeightKey as String: UIScreen.main.bounds.height
        ]
        let adaptorAttributes = [
            kCVPixelBufferPixelFormatTypeKey as String: kCVPixelFormatType_32ARGB,
            kCVPixelBufferWidthKey as String: UIScreen.main.bounds.width,
            kCVPixelBufferHeightKey as String: UIScreen.main.bounds.height,
            kCVPixelFormatOpenGLESCompatibility as String: kCFBooleanTrue!
        ]
        pixelBufferAdaptor = AVAssetWriterInputPixelBufferAdaptor(assetWriterInput: videoInput, sourcePixelBufferAttributes: pixelBufferAttributes, pixelBufferPool: nil, pixelBufferAttributes: adaptorAttributes)
        
        // 创建文件路径
        let documentsPath = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true)[0]
        let videoOutputFilePath = documentsPath + "/output.mp4"
        let videoOutputFileURL = URL(fileURLWithPath: videoOutputFilePath)
        do {
            recorder = try AVAssetWriter(outputURL: videoOutputFileURL, fileType: .mp4)
        } catch {
            print("Failed to create AVAssetWriter: \(error)")
            return
        }
        
        // 添加视频输入
        if recorder.canAdd(videoInput) {
            recorder.add(videoInput)
        } else {
            print("Failed to add video input to AVAssetWriter")
            return
        }
        
        // 开始AR会话
        let configuration = ARWorldTrackingConfiguration()
        arSession.run(configuration)
    }

    // ARSessionDelegate方法：每帧渲染回调
    func session(_ session: ARSession, didUpdate frame: ARFrame) {
        // 判断是否正在录制
        if isRecording {
            // 将AR会话帧转换为CVPixelBuffer
            guard let pixelBufferPool = pixelBufferAdaptor.pixelBufferPool else {
                print("Failed to get pixel buffer pool")
                return
            }
            var pixelBuffer: CVPixelBuffer?
            let status = CVPixelBufferPoolCreatePixelBuffer(nil, pixelBufferPool, &pixelBuffer)
            if status != kCVReturnSuccess {
                print("Failed to create pixel buffer")
                return
            }
            CVPixelBufferLockBaseAddress(pixelBuffer!, CVPixelBufferLockFlags(rawValue: 0))
            let pixelData = CVPixelBufferGetBaseAddress(pixelBuffer!)
            let rgbColorSpace = CGColorSpaceCreateDeviceRGB()
            let context = CGContext(data: pixelData, width: Int(UIScreen.main.bounds.width), height: Int(UIScreen.main.bounds.height), bitsPerComponent: 8, bytesPerRow: CVPixelBufferGetBytesPerRow(pixelBuffer!), space: rgbColorSpace, bitmapInfo: CGImageAlphaInfo.premultipliedFirst.rawValue)
            context?.translateBy(x: 0, y: UIScreen.main.bounds.height)
            context?.scaleBy(x: 1.0, y: -1.0)
            UIGraphicsPushContext(context!)
            view.layer.render(in: context!)
            UIGraphicsPopContext()
            CVPixelBufferUnlockBaseAddress(pixelBuffer!, CVPixelBufferLockFlags(rawValue: 0))
            
            // 将CVPixelBuffer添加到AVAssetWriterInputPixelBufferAdaptor中
            if let pixelBuffer = pixelBuffer {
                let frameTime = frame.timestamp
                pixelBufferAdaptor.append(pixelBuffer, withPresentationTime: frameTime)