UIDeviceOrientationを基準にしたUIImageOrientationとAVCaptureVideoOrientationの向き対応

AvFoundationなんかで遊んでいる時にデバイスの向きとカメラの向きで頭がこんがらがります。
背面カメラはそのまま、前面カメラはミラー前提です。

UIImageOrientation

- (UIImageOrientation)currentImageOrientation {
    UIDeviceOrientation deviceOrientation = [[UIDevice currentDevice] orientation];

    // 背面カメラチェック
    BOOL IsBack = [[_activeVideoInput device] position] ==AVCaptureDevicePositionBack;

    switch (deviceOrientation) {
        case UIDeviceOrientationLandscapeLeft:
            return IsBack ?  UIImageOrientationUp:UIImageOrientationDownMirrored;
            break;
        case UIDeviceOrientationLandscapeRight:
            return IsBack? UIImageOrientationDown :UIImageOrientationUpMirrored;
            break;
        case UIDeviceOrientationPortrait:
            return IsBack ?  UIImageOrientationRight:UIImageOrientationLeftMirrored;
            break;
        case UIDeviceOrientationPortraitUpsideDown:
            return IsBack ? UIImageOrientationLeft : UIImageOrientationRightMirrored;
            break;
        default:
            return UIImageOrientationRight;
            break;
    }
}

AVCaptureVideoOrientation

- (AVCaptureVideoOrientation)currentVideoOrientation {
    UIDeviceOrientation deviceOrientation = [[UIDevice currentDevice] orientation];

    switch (deviceOrientation) {
        case UIDeviceOrientationLandscapeLeft:
            return AVCaptureVideoOrientationLandscapeRight;
            break;
        case UIDeviceOrientationLandscapeRight:
            return AVCaptureVideoOrientationLandscapeLeft;
            break;
        case UIDeviceOrientationPortrait:
            return AVCaptureVideoOrientationPortrait;
            break;
        case UIDeviceOrientationPortraitUpsideDown:
            return AVCaptureVideoOrientationPortraitUpsideDown;
            break;
        default:
            return AVCaptureVideoOrientationLandscapeRight;
            break;
    }
}