iOS集成WebRTC时RTCMTLVideoView无画面问题排查求助

我正在iOS应用中集成WebRTC视频功能，已从官方渠道下载源码并成功编译。因该版本不支持GLView，改用MetalKit引入RTCMTLVideoView，同时实现了RTCVideoRenderer与RTCVideoViewDelegate并设置self.metalVideoView.delegate = self。

收到视频时，通知对象显示为RTC_OBJC_TYPE(RTCMediaStreamTrack): video janusv0 enabled Live，且VideoTracks数量为1，但屏幕仅显示空白画面。此前用GLView时相同逻辑可正常运行。

以下是处理视频接收的代码：

@objc func handleFloorPlanVideoReceived(_ notification: Notification?) {
    if let remoteVideoTrack = notification?.object as? RTCVideoTrack {

        print("Recieved Remote Video: \(remoteVideoTrack)")

        DispatchQueue.main.async {
            // Initialize the metalVideoView
            self.metalVideoView = RTCMTLVideoView(frame: CGRect.zero)
            self.metalVideoView.delegate = self

            // Add the metalVideoView to the view hierarchy
            self.view.addSubview(self.metalVideoView)
            self.metalVideoView.backgroundColor = .edgeGray
            self.metalVideoView.videoContentMode = .scaleAspectFit

            // Set up auto layout constraints
            self.metalVideoView.translatesAutoresizingMaskIntoConstraints = false
            NSLayoutConstraint.activate([
                self.metalVideoView.topAnchor.constraint(equalTo: self.view.safeAreaLayoutGuide.topAnchor),
                self.metalVideoView.leadingAnchor.constraint(equalTo: self.view.leadingAnchor),
                self.metalVideoView.trailingAnchor.constraint(equalTo: self.view.trailingAnchor),
                self.metalVideoView.heightAnchor.constraint(equalTo: self.view.heightAnchor, multiplier: 1.0/3.0)
            ])

            remoteVideoTrack.add(self.metalVideoView)

            // Create and add the UIActivityIndicatorView
            let activityIndicator = UIActivityIndicatorView(style: .large)
            activityIndicator.color = .white
            self.metalVideoView.addSubview(activityIndicator)
            self.activityIndicator = activityIndicator

            // Set up constraints for the activity indicator
            activityIndicator.translatesAutoresizingMaskIntoConstraints = false
            NSLayoutConstraint.activate([
                activityIndicator.centerXAnchor.constraint(equalTo: self.metalVideoView.centerXAnchor),
                activityIndicator.centerYAnchor.constraint(equalTo: self.metalVideoView.centerYAnchor)
            ])

            activityIndicator.startAnimating()

            // Create and add the close button
            let closeButton = UIButton(type: .system)
            if let closeImage = UIImage(systemName: "xmark") {
                closeButton.setImage(closeImage, for: .normal)
            }

            self.metalVideoView.addSubview(closeButton)

            // Set up constraints for the close button
            closeButton.translatesAutoresizingMaskIntoConstraints = false
            NSLayoutConstraint.activate([
                closeButton.topAnchor.constraint(equalTo: self.metalVideoView.topAnchor, constant: 8),
                closeButton.trailingAnchor.constraint(equalTo: self.metalVideoView.trailingAnchor, constant: -8)
            ])

            // Add target for close button tap event
            closeButton.addTarget(self, action: #selector(self.closeButtonTapped), for: .touchUpInside)

            self.metalVideoView.setNeedsLayout()
        }
    }
}

• 避免重复创建视图实例：当前每次收到视频通知都会重新初始化metalVideoView，会导致之前的渲染上下文被重置。建议提前在viewDidLoad等生命周期方法中创建好metalVideoView并添加到视图层级，仅在收到视频轨道时执行remoteVideoTrack.add(self.metalVideoView)。

• 补全RTCVideoViewDelegate方法：必须实现videoView:didChangeVideoSize:方法，该回调会触发视图根据视频尺寸调整渲染逻辑，缺失可能导致画面无法显示：

  func videoView(_ videoView: RTCMTLVideoView, didChangeVideoSize size: CGSize) {
      // 可选：根据视频尺寸更新视图约束或布局
  }
  

• 验证视频帧接收：在RTCVideoRenderer的renderFrame:方法中添加日志，确认是否有视频帧传入：

  func renderFrame(_ frame: RTCVideoFrame?) {
      guard let frame = frame else { return }
      print("收到视频帧：分辨率\(frame.width)x\(frame.height)")
  }
  

• 移除冗余布局调用：self.metalVideoView.setNeedsLayout()在Auto Layout约束激活后是多余的，系统会自动处理布局更新，可删除该代码。

• 检查线程安全：确保所有与RTCMTLVideoView相关的操作都在主线程执行（当前代码已通过DispatchQueue.main.async处理，这部分符合要求）。

内容的提问来源于stack exchange，提问作者Sergey Z