iPad 上横向模式下的 AVCaptureSession 问题

Question

我一直在尝试从前置摄像头捕捉帧并将其呈现在视图上。这是我的代码

_session = [[AVCaptureSession alloc] init];
_session.sessionPreset = AVCaptureSessionPreset640x480;

AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
NSError *error = nil;
AVCaptureDeviceInput *deviceInput = [[AVCaptureDeviceInput alloc] initWithDevice:device error:&error];

if (deviceInput) {
    [_session addInput:deviceInput];
}
else {
    DDLogInfo(@"Some wierd shit happened");
    return;
}

// Session output
/*
AVCaptureMetadataOutput *output = [[AVCaptureMetadataOutput alloc] init];
[output setMetadataObjectsDelegate:self queue:dispatch_get_main_queue()];
[_session addOutput:output];
output.metadataObjectTypes = @[AVMetadataObjectTypeFace];
AVCaptureConnection *connection = [output connectionWithMediaType:AVMediaTypeMetadata];
connection.videoOrientation = AVCaptureVideoOrientationLandscapeLeft;
*/

// Session output
AVCaptureMovieFileOutput *videoOutput = [[AVCaptureMovieFileOutput alloc] init];
[_session addOutput:videoOutput];
AVCaptureConnection *connection = [videoOutput connectionWithMediaType:AVMediaTypeVideo];
connection.videoOrientation = AVCaptureVideoOrientationPortrait;

// Preview layer
_previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:_session];
_previewLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;
_previewLayer.frame = CGRectMake(0, 0, self.middleView.frame.size.width, self.middleView.frame.size.height);
[self.middleView.layer addSublayer:_previewLayer];

[_session startRunning];

问题是，当我的 iPad 是横向时，表示层上的图像旋转了 90 度。我该如何解决？我一直在浏览堆栈溢出，试图用AVCaptureConnection 做点什么，可惜无济于事。

Answer 1

解决了，现在它可以在各个方向工作。我们需要设置这个

_previewLayer.connection.videoOrientation = [self videoOrientationFromCurrentDeviceOrientation];

方法在哪里：

 - (AVCaptureVideoOrientation) videoOrientationFromCurrentDeviceOrientation {
switch (self.interfaceOrientation) {
    case UIInterfaceOrientationPortrait: {
        return AVCaptureVideoOrientationPortrait;
    }
    case UIInterfaceOrientationLandscapeLeft: {
        return AVCaptureVideoOrientationLandscapeLeft;
    }
    case UIInterfaceOrientationLandscapeRight: {
        return AVCaptureVideoOrientationLandscapeRight;
    }
    case UIInterfaceOrientationPortraitUpsideDown: {
        return AVCaptureVideoOrientationPortraitUpsideDown;
    }
}
}

还有我们需要设置的捕获输出：

AVCaptureConnection *output2VideoConnection = [videoOutput connectionWithMediaType:AVMediaTypeVideo];
output2VideoConnection.videoOrientation = [self videoOrientationFromCurrentDeviceOrientation];

Answer 2

在 Swift 3 中：

首先我们必须像 MegaManX 一样设置previewLayer.connection.videoOrientation

previewLayer.connection.videoOrientation = self.videoOrientationFromCurrentDeviceOrientation()

方法在哪里：

func videoOrientationFromCurrentDeviceOrientation() -> AVCaptureVideoOrientation {
    switch UIApplication.shared.statusBarOrientation {
    case .portrait:
        return AVCaptureVideoOrientation.portrait
    case .landscapeLeft:
        return AVCaptureVideoOrientation.landscapeLeft
    case .landscapeRight:
        return AVCaptureVideoOrientation.landscapeRight
    case .portraitUpsideDown:
        return AVCaptureVideoOrientation.portraitUpsideDown
    default:
        // Can this happen?
        return AVCaptureVideoOrientation.portrait
    }
}

那么我们还要处理用户旋转设备时的videoOrientation（方法来自here）

override func viewWillTransition(to size: CGSize, with coordinator: UIViewControllerTransitionCoordinator) {

    coordinator.animate(alongsideTransition: { (UIViewControllerTransitionCoordinatorContext) -> Void in
        self.previewLayer.connection.videoOrientation = self.videoOrientationFromCurrentDeviceOrientation()

        }, completion: { (UIViewControllerTransitionCoordinatorContext) -> Void in
            // Finish Rotation
    })

    super.viewWillTransition(to: size, with: coordinator)
}