在ipad上，用户是横屏操作的，虽然界面旋转了，是横屏的，但是摄像头里显示的依然是竖屏效果，也就是说从摄像头里看到的和人眼看到的内容相差90度或者270度，网上搜索了一番，是这个AVCaptureVideoPreviewLayer 的问题，设备旋转了，但是它没有旋转，导致屏幕显示的，和人眼看到的有偏差，找到如下解决办法，希望对大家有帮助
AVCaptureVideoPreviewLayer *layer = [AVCaptureVideoPreviewLayer layerWithSession:_captureSession];
layer.videoGravity = AVLayerVideoGravityResizeAspectFill;
layer.frame= view.frame;
[view.layer insertSublayer:layer atIndex:0];
CGRectlayerRect = view.layer.bounds;//获取当前设备的旋转角度
UIDeviceOrientation deorientation =[[UIDevice currentDevice] orientation];
switch(deorientation) {
case UIDeviceOrientationLandscapeLeft:
layer.affineTransform = CGAffineTransformMakeRotation(M_PI+ M_PI_2);// 270 degrees
//旋转270度和90度的效果是一样的，设备旋转之后，屏幕宽和高对换了，那么摄像头的layer的宽高也应该对换
[layer setBounds:CGRectMake(0,0, layerRect.size.height, layerRect.size.width)];
break;
case UIDeviceOrientationLandscapeRight:
layer.affineTransform = CGAffineTransformMakeRotation(M_PI_2);
// 90 degrees
[layer setBounds:CGRectMake(0,0, layerRect.size.height, layerRect.size.width)];
break;
case UIDeviceOrientationPortraitUpsideDown:
layer.affineTransform = CGAffineTransformMakeRotation(M_PI);
// 180 degrees
//设备正着和倒着都是竖屏，宽高没变化，那么摄像头的layer的宽高也还是屏幕的宽高
[layer setBounds:layerRect];
break;
default:
{
layer.affineTransform = CGAffineTransformMakeRotation(0.0);
[layer setBounds:layerRect];
}
break;
}
[layer setPosition:CGPointMake(CGRectGetMidX(layerRect),CGRectGetMidY(layerRect))];
