无法在Swift操场上捕获视频数据，captureOutput AVCaptureVideoDataOutputSampleBufferDelegate委托方法未调用

I want to get access to the iPad's camera on the Swift Playgrounds iPad app. I have found that it's not possibile to capture video data, even though my playground runs ok.

我想通过Swift Playgrounds(场地)iPad应用程序使用iPad的摄像头。我发现，虽然我的游乐场运行正常，但我不可能采集视频数据。

captureOutput(_ captureOutput: AVCaptureOutput!, didOutputSampleBuffer sampleBuffer: CMSampleBuffer!, from connection: AVCaptureConnection!), a delegate method of the AVCaptureVideoDataOutputSampleBufferDelegate protocol, is not getting called (probably because no video data is coming in), while it is in my iOS app.

captureOutput(_ captureOutput:AVCaptureOutput !,didOutputSampleBuffer sampleBuffer:CMSampleBuffer !在我的iOS应用中，AVCaptureVideoDataOutputSampleBufferDelegate协议的委托方法不会被调用(可能是因为没有视频数据输入)。

The view in my playground is supposed to display the FaceTime camera view. Why can't I display the camera output even though Apple explicitly says it's allowed to do so? Also, the Playground app asks me for camera permissions as soon as I open my playground, so it should be allowed in some way.

我操场上的视图应该显示FaceTime摄像头的视图。为什么我不能显示相机的输出，即使苹果明确表示允许这样做?另外，当我打开我的游乐场时，游乐场应用会问我是否有摄像头权限，所以应该允许。

import UIKit
import CoreImage
import AVFoundation
import ImageIO
import PlaygroundSupport

class Visage: NSObject, AVCaptureVideoDataOutputSampleBufferDelegate {

    var visageCameraView : UIView = UIView()
    fileprivate var faceDetector : CIDetector?
    fileprivate var videoDataOutput : AVCaptureVideoDataOutput?
    fileprivate var videoDataOutputQueue : DispatchQueue?
    fileprivate var cameraPreviewLayer : AVCaptureVideoPreviewLayer?
    fileprivate var captureSession : AVCaptureSession = AVCaptureSession()
    fileprivate let notificationCenter : NotificationCenter = NotificationCenter.default

    override init() {
        super.init()

        self.captureSetup(AVCaptureDevicePosition.front)
        var faceDetectorOptions : [String : AnyObject]?
        faceDetectorOptions = [CIDetectorAccuracy : CIDetectorAccuracyHigh as AnyObject]
        self.faceDetector = CIDetector(ofType: CIDetectorTypeFace, context: nil, options: faceDetectorOptions)
    }

    func beginFaceDetection() {
        self.captureSession.startRunning()
    }

    func endFaceDetection() {
        self.captureSession.stopRunning()
    }

    fileprivate func captureSetup (_ position : AVCaptureDevicePosition) {
        var captureError : NSError?
        var captureDevice : AVCaptureDevice!

        for testedDevice in AVCaptureDevice.devices(withMediaType: AVMediaTypeVideo){
            if ((testedDevice as AnyObject).position == position) {
                captureDevice = testedDevice as! AVCaptureDevice
            }
        }

        if (captureDevice == nil) {
            captureDevice = AVCaptureDevice.defaultDevice(withMediaType: AVMediaTypeVideo)
        }

        var deviceInput : AVCaptureDeviceInput?
        do {
            deviceInput = try AVCaptureDeviceInput(device: captureDevice)
        } catch let error as NSError {
            captureError = error
            deviceInput = nil
        }
        captureSession.sessionPreset = AVCaptureSessionPresetHigh

        if (captureError == nil) {
            if (captureSession.canAddInput(deviceInput)) {
                captureSession.addInput(deviceInput)
            }

            self.videoDataOutput = AVCaptureVideoDataOutput()
            self.videoDataOutput!.videoSettings = [kCVPixelBufferPixelFormatTypeKey as AnyHashable: Int(kCVPixelFormatType_32BGRA)]
            self.videoDataOutput!.alwaysDiscardsLateVideoFrames = true
            self.videoDataOutputQueue = DispatchQueue(label: "VideoDataOutputQueue", attributes: [])
            self.videoDataOutput!.setSampleBufferDelegate(self, queue: self.videoDataOutputQueue!)

            if (captureSession.canAddOutput(self.videoDataOutput)) {
                captureSession.addOutput(self.videoDataOutput)
            }
        }

        visageCameraView.frame = UIScreen.main.bounds
        let previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)
        previewLayer?.frame = UIScreen.main.bounds
        previewLayer?.videoGravity = AVLayerVideoGravityResizeAspectFill
        visageCameraView.layer.addSublayer(previewLayer!)
    }

    // NOT CALLED
    func captureOutput(_ captureOutput: AVCaptureOutput!, didOutputSampleBuffer sampleBuffer: CMSampleBuffer!, from connection: AVCaptureConnection!) {            
        print("delegate method called!")
    }
}

class SmileView: UIView {
    let smileView = UIView()
    var smileRec: Visage!

    override init(frame: CGRect) {
        super.init(frame: frame)
        self.addSubview(smileView)
        self.translatesAutoresizingMaskIntoConstraints = false
        smileRec = Visage()
        smileRec.beginFaceDetection()
        let cameraView = smileRec.visageCameraView
        self.addSubview(cameraView)
    }

    required init?(coder aDecoder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
}

let frame = CGRect(x: 0, y: 0, width: UIScreen.main.bounds.width, height: UIScreen.main.bounds.height)
let sView = SmileView(frame: frame)
PlaygroundPage.current.liveView = sView

2 个解决方案

#1

Edit: this should have been fixed :)

编辑:这应该是固定的:)

- - -

Edit: this was confirmed to be a bug by Apple.

编辑:这被苹果证实是一个错误。

I have filed a bug report and I will update this answer when new official information comes in.

我已经提交了一个bug报告，当新的官方信息出现时我会更新这个答案。

#2

I think you need to set the needsIndefiniteExecution property so that execution is not stopped after your code is completed. From apple:

我认为您需要设置needsIndefiniteExecution属性，以便在代码完成后不会停止执行。从苹果公司:

By default, all top-level code is executed, and then execution is terminated. When working with asynchronous code, enable indefinite execution to allow execution to continue after the end of the playground’s top-level code is reached. This, in turn, gives threads and callbacks time to execute.

默认情况下，执行所有*代码，然后终止执行。当使用异步代码时，允许不确定的执行，以便在达到游乐场的*代码的末尾之后继续执行。这反过来又给线程和回调时间来执行。

Editing the playground automatically stops execution, even when indefinite execution is enabled.

编辑游乐场自动停止执行，即使不确定执行被启用。

Set needsIndefiniteExecution to true to continue execution after the end of top-level code. set it to false to stop execution at that point.

将needsIndefiniteExecution设置为true，在*代码结束后继续执行。将其设置为false，以在此时停止执行。

So possible code at the end will be :

所以最后可能的代码是:

let frame = CGRect(x: 0, y: 0, width: UIScreen.main.bounds.width, height: UIScreen.main.bounds.height)
let sView = SmileView(frame: frame)
PlaygroundPage.current.needsIndefiniteExecution = true
PlaygroundPage.current.liveView = sView

#1