ios - AVFoundation 切换相机速度慢(连接到样本缓冲区)

Question

override func viewDidLoad() {
    super.viewDidLoad()
    ...
    setupDevice()
    setupInputOutput()
}

查看加载是否启动设置链

 func setupDevice() {
    let deviceDiscoverySession = AVCaptureDevice.DiscoverySession(deviceTypes: [AVCaptureDevice.DeviceType.builtInWideAngleCamera], mediaType: AVMediaType.video, position: AVCaptureDevice.Position.unspecified)
    let devices = deviceDiscoverySession.devices

    for device in devices {
        if device.position == AVCaptureDevice.Position.back {
            backCamera = device
            setupCorrectFramerate(currentCamera: backCamera!)
        }
        else if device.position == AVCaptureDevice.Position.front {
            frontCamera = device
            setupCorrectFramerate(currentCamera: frontCamera!)
        }
    }
    currentCamera = cameraModeIsBack ? backCamera : frontCamera
}

var deviceInput: AVCaptureDeviceInput?
let videoOutput = AVCaptureVideoDataOutput()

func setupInputOutput() {
    do {
        let captureDeviceInput = try AVCaptureDeviceInput(device: currentCamera!)
        deviceInput = captureDeviceInput
        captureSession.sessionPreset = AVCaptureSession.Preset.hd1280x720

        if captureSession.canAddInput(deviceInput!) {
            captureSession.addInput(deviceInput!)
        }
        videoOutput.setSampleBufferDelegate(self, queue: DispatchQueue(label: "sample buffer delegate", attributes: []))
        if captureSession.canAddOutput(videoOutput) {
            captureSession.addOutput(videoOutput)
        }
        captureSession.startRunning()
        if(firstTime){
            setupMetal()
        }
        firstTime = false
        toggleCamerButton.isEnabled = true
    } catch {
        print(error)
    }
}

在较高级别上，我找到设备输入，设置其帧速率并设置捕获 session (缓冲区输出被处理到 MTKView)。

问题是当我更换相机时。它要么是快速且不连续，要么是变得非常慢并且在响应之前卡住 4-5 秒。

我用来更改相机的逻辑:

func updateCameras(){
    DispatchQueue.global().async {
        self.captureSession.stopRunning()
        self.captureSession.removeInput(self.deviceInput!)
        self.currentCamera = self.cameraModeIsBack ? self.backCamera : self.frontCamera
        self.changeCameras()
    }
}


func changeCameras(){
    do {
        let captureDeviceInput = try AVCaptureDeviceInput(device: self.currentCamera!)
        self.deviceInput = captureDeviceInput
        if self.captureSession.canAddInput(self.deviceInput!) {
            self.captureSession.addInput(self.deviceInput!)
        }
        self.captureSession.startRunning()
       DispatchQueue.main.async {
            self.toggleCamerButton.isEnabled = true
       }
    } catch {
        print(error)
    }

}

我已经尽可能地修改了它。切换相机本质上是

1. 停止摄像头 session
2. 删除输入
3. 添加输入
4. 开始 session

我不知道为什么它的变化如此之大(大部分时间在我的 iPhone X 上运行良好，而在我的 iPhone 6 上却总是很慢)。

Answer 1

我怀疑操作cameraSession的调用应该在主线程上完成。尝试更改 updateCameras() 以使用 DispatchQueue.main.async() 而不是 DispatchQueue.global().async

像这样:

func updateCameras(){
    DispatchQueue.main.async {
        self.captureSession.stopRunning()
        self.captureSession.removeInput(self.deviceInput!)
        self.currentCamera = self.cameraModeIsBack ? self.backCamera : self.frontCamera
        self.changeCameras()
    }
}

完成此更改后，将不再需要 changeCameras() 函数中对 DispatchQueue.main.async() 的调用