Crash when using front camera ONLY on pre-iPhone 7 devices

问题

I've recently started running beta on my camera-based app. Everything is working as expected except on iPhone 6 devices.

The session starts on the back camera, and each time an iPhone 6 user switches to the front camera the app crashes. (And just to be really clear: no one on any other iPhone model is experiencing the issue.) I've gotten my hands on a 6 to test and can consistently reproduce the error, resulting in libc++abi.dylib: terminating with uncaught exception of type NSException.

I've tried starting the session on the front camera and it crashes immediately.

func initializeCamera() {
    self.captureSession.sessionPreset = .hd1920x1080

    let discovery = AVCaptureDevice.DiscoverySession.init(deviceTypes: [AVCaptureDevice.DeviceType.builtInWideAngleCamera],
                                                          mediaType: .video,
                                                          position: .unspecified) as AVCaptureDevice.DiscoverySession

    for device in discovery.devices as [AVCaptureDevice] {
        if device.hasMediaType(.video) {
            if device.position == AVCaptureDevice.Position.front {
                videoCaptureDevice = device
                do {
                    try currentDeviceInput = AVCaptureDeviceInput(device: device)
                } catch {
                    print("error: \(error.localizedDescription)")
                }
            }
        }
    }

    if videoCaptureDevice != nil {
        do {
            let videoInput = try AVCaptureDeviceInput(device: videoCaptureDevice!)
            captureSession.addInput(videoInput)

            if let audioInput = AVCaptureDevice.default(for: .audio) {
                try captureSession.addInput(AVCaptureDeviceInput(device: audioInput))
            }

            previewLayer = AVCaptureVideoPreviewLayer(session: captureSession)

            guard let previewLayer = previewLayer else { return }

            cameraPreviewView.frame = cameraContainer.frame

            cameraPreviewView.layer.addSublayer(previewLayer)
            previewLayer.frame = cameraPreviewView.frame

            previewLayer.videoGravity = AVLayerVideoGravity.resizeAspectFill

            setVideoOrientation()

            captureSession.addOutput(movieFileOutput)

            if let movieFileOutputConnection = movieFileOutput.connection(with: .video) {
                if movieFileOutputConnection.isVideoStabilizationSupported {
                    movieFileOutputConnection.preferredVideoStabilizationMode = .cinematic
                }
            }

            captureSession.startRunning()

            sessionIsReady(true)

        } catch {
            print("error: \(error.localizedDescription)")
        }
    }

}
func setVideoOrientation() {
    if let connection = self.previewLayer?.connection {
        if connection.isVideoOrientationSupported {
            connection.videoOrientation = .portrait
            previewLayer?.frame = cameraContainer.bounds
        }
    }
}

The crash is triggered at captureSession.addInput(videoInput). videoInput is not nil. The camera's orientation is locked to portrait.

Can anyone offer any insight? Please let me know if any additional code would be helpful. Thanks in advance.

回答1:

captureSession.addInput(videoInput) is causing the crash.

So you should use canAddInput(_:) before to avoid the crash.

if captureSession.canAddInput(videoInput) {
    captureSession.addInput(videoInput)
}

And in your case, captureSession.canAddInput(videoInput) == false with that iPhone 6.

Now, you are also doing self.captureSession.sessionPreset = .hd1920x1080

But according to WikiPedia, the iPhone 6 Front Camera hardware supports camera 1.2 MP (1280×960 px max.), 720p video recording (30 fps). Doesn't seem to fit the 1920*1080 ("Full HD").

You could do this check what the "max" AVCaptureSession.Preset you can use.

func setSessionPreset(forDevice device: AVCaptureDevice) {
    let videoPresets: [AVCaptureSession.Preset] = [.hd4K3840x2160, .hd1920x1080, .hd1280x720] //etc. Put them in order to "preferred" to "last preferred"
    let preset = videoPresets.first(where: { device.supportsSessionPreset($0) }) ?? .hd1280x720
    captureSession.sessionPreset = preset
}

来源：https://stackoverflow.com/questions/53213054/crash-when-using-front-camera-only-on-pre-iphone-7-devices

标签

ios

swift

avfoundation

avcapturesession