iOS摄像头采集会话代码在iOS正常但Catalyst环境崩溃

问题描述 #

以下用于配置AVCaptureSession视频输入输出的代码在iOS平台运行完全正常：

let videoOutput = AVCaptureVideoDataOutput()

guard let cameraDevice = device.device,
      let captureDeviceInput = try? AVCaptureDeviceInput(device: cameraDevice),
      self.canAddInput(captureDeviceInput),
      self.canAddOutput(videoOutput) else {
    log("FrameExtractor error: could not setup input or output.")
    return
}

self.addInput(captureDeviceInput)
videoOutput.setSampleBufferDelegate(self, queue: DispatchQueue(label: "sample buffer"))
self.addOutput(videoOutput)

guard let connection = videoOutput.connection(with: CAMERA_FEED_MEDIA_TYPE),
      connection.isVideoOrientationSupported,
      connection.isVideoMirroringSupported else {
    log("FrameExtractor: configureSession: Cannot establish connection")
    return
}

if let videoOrientation = getCameraOrientation(device: device) {
    connection.videoOrientation = videoOrientation
}

// Mirroring the front camera normalizes the display output for iPad's front camera
connection.isVideoMirrored = position == .front

但在Catalyst环境中运行时，执行self.addOutput(videoOutput)会持续崩溃，报错信息翻译如下：

应用因未捕获的异常NSInternalInconsistencyException终止，原因：无效参数，不满足条件：index>=0 && index<[_currentItems count]

问题原因与修复方案 #

• 核心原因：Catalyst环境下AVCaptureSession的配置逻辑与纯iOS存在差异，默认配置兼容性不足，且会话状态管理、输入输出添加顺序的要求更严格。
• 修复步骤：
  1. 提前设置视频输出格式：Catalyst对视频像素格式的兼容性要求更高，添加输出前显式指定兼容格式：

     let videoSettings: [String: Any] = [
         kCVPixelBufferPixelFormatTypeKey as String: kCVPixelFormatType_32BGRA
     ]
     videoOutput.videoSettings = videoSettings
     

  2. 开启丢弃迟滞帧：避免Catalyst环境下帧队列溢出引发异常：

     videoOutput.alwaysDiscardsLateVideoFrames = true
     

  3. 调整输入输出添加顺序：先添加输出，再添加输入（部分Catalyst版本存在顺序依赖问题）：

     self.addOutput(videoOutput)
     self.addInput(captureDeviceInput)
     

  4. 确保会话处于停止状态：添加输入输出前先停止会话，避免状态冲突：

     self.stopRunning()
     

修复后完整代码示例 #

let videoOutput = AVCaptureVideoDataOutput()

// 配置视频输出参数
let videoSettings: [String: Any] = [
    kCVPixelBufferPixelFormatTypeKey as String: kCVPixelFormatType_32BGRA
]
videoOutput.videoSettings = videoSettings
videoOutput.alwaysDiscardsLateVideoFrames = true

guard let cameraDevice = device.device,
      let captureDeviceInput = try? AVCaptureDeviceInput(device: cameraDevice),
      self.canAddInput(captureDeviceInput),
      self.canAddOutput(videoOutput) else {
    log("FrameExtractor error: could not setup input or output.")
    return
}

// 确保会话处于停止状态
self.stopRunning()

// 先添加输出，再添加输入
self.addOutput(videoOutput)
self.addInput(captureDeviceInput)

videoOutput.setSampleBufferDelegate(self, queue: DispatchQueue(label: "sample buffer"))

guard let connection = videoOutput.connection(with: CAMERA_FEED_MEDIA_TYPE),
      connection.isVideoOrientationSupported,
      connection.isVideoMirroringSupported else {
    log("FrameExtractor: configureSession: Cannot establish connection")
    return
}

if let videoOrientation = getCameraOrientation(device: device) {
    connection.videoOrientation = videoOrientation
}

connection.isVideoMirrored = position == .front

// 按需重新启动会话
self.startRunning()

内容的提问来源于stack exchange，提问作者narner