AVCaptureVideoDataOutput captureOutput没有被调用 [英] AVCaptureVideoDataOutput captureOutput not being called

问题描述

我正在尝试在具有AVCaptureScreenInput的Mac上进行屏幕捕获，但是从未调用过AVCaptureVideoDataOutput委托captureCapture，而且我不确定为什么.我确实收到一条通知，说捕获会话已开始.

I'm trying screen capture on a Mac with AVCaptureScreenInput, but AVCaptureVideoDataOutput delegate captureOutput is never called, and I'm not sure why. I do get a notification saying the capture session was started.

import Cocoa
import AVFoundation

class ViewController: NSViewController, AVCaptureVideoDataOutputSampleBufferDelegate {

    var captureSession: AVCaptureSession!

    override func viewDidLoad() {
        super.viewDidLoad()
        // Do any additional setup after loading the view.
    }

    override func viewWillAppear() {
        super.viewWillAppear()
        NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(ViewController.errorNotif), name: AVCaptureSessionRuntimeErrorNotification, object: nil)
        NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(ViewController.startedNotif), name: AVCaptureSessionDidStartRunningNotification, object: nil)
        startScreenCapture()
    }

    override func viewWillDisappear() {
        super.viewWillDisappear()
        NSNotificationCenter.defaultCenter().removeObserver(self)
    }

    func captureOutput(captureOutput: AVCaptureOutput!, didDropSampleBuffer sampleBuffer: CMSampleBuffer!, fromConnection connection: AVCaptureConnection!) {
        print("ignore frame, add code to handle later")
    }

    func startScreenCapture() {

        let displayId = CGMainDisplayID()
        captureSession = AVCaptureSession()
        if captureSession.canSetSessionPreset(AVCaptureSessionPresetHigh) {
            captureSession.sessionPreset = AVCaptureSessionPresetHigh
        }
        let captureScreenInput = AVCaptureScreenInput(displayID: displayId)
        if captureSession.canAddInput(captureScreenInput) {
            captureSession.addInput(captureScreenInput)
        } else {
            print("Could not add main display to capture input")
        }

        let output = AVCaptureVideoDataOutput()

        let queue = dispatch_queue_create("myQueue", DISPATCH_QUEUE_SERIAL)
        output.setSampleBufferDelegate(self, queue: queue)
        output.alwaysDiscardsLateVideoFrames = true

        output.videoSettings = [kCVPixelBufferPixelFormatTypeKey as NSString: NSNumber(unsignedInt: kCVPixelFormatType_32BGRA)]
        captureSession.addOutput(output)
        captureSession.startRunning()
    }

    func errorNotif() {
        print("error starting capture")
    }
    func startedNotif() {
        print("started screen capture")
    }
}

推荐答案

您需要定义didOutputSampleBuffer委托回调以实际接收捕获的帧:

You need to define the didOutputSampleBuffer delegate callback to actually receive the captured frames:

func captureOutput(captureOutput: AVCaptureOutput!, didOutputSampleBuffer sampleBuffer: CMSampleBuffer!, fromConnection connection: AVCaptureConnection!) {
    print("captured \(sampleBuffer)")
}

p.s.我不确定macOS，但是viewWillAppear可能不是进行初始化的好地方，因为至少在iOS上可以多次调用.

p.s. I'm not sure about macOS, but viewWillAppear may not be a good place to do initialisation because on iOS at least it can be called multiple times.

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