Iphone 如何更改AVCaptureVideoPreviewLayer帧高度和宽度

请帮助我如何更改AVCaptureVideoPreviewLayer帧大小和大小

我通过

Height=100px；宽度=300px

如果我通过高度大小100，则宽度不更改为300px

以下是代码：

    AVCaptureVideoPreviewLayer *previewLayer = [AVCaptureVideoPreviewLayer layerWithSession:session];
    previewLayer.frame = CGRectMake(20, 50, 300, 100);
    self.view.frame=CGRectMake(20, 50, 300, 100);


    CGRect layerRect = [[[self view] layer] bounds];
    [previewLayer setBounds:layerRect];
    [previewLayer setPosition:CGPointMake(CGRectGetMidX(layerRect),CGRectGetMidY(layerRect))];
    [[[self view] layer] addSublayer:previewLayer];
    [previewView.layer addSublayer:previewLayer];

然后：

就这样

@property (nonatomic, retain) AVCaptureVideoPreviewLayer *prevLayer;

self.prevLayer = [AVCaptureVideoPreviewLayer layerWithSession: self.captureSession];
    self.prevLayer.frame = yourRect;
[self.view.layer addSublayer: self.prevLayer];