AVCaptureDevice videoZoomFactor

Question

我正在用我的相机做一个使用AVFoundation/AVFoundation.h的项目。现在，我想实现屏幕的缩放。

我在AVCaptureDevice上查看了文档，发现了一个名为"videoZoomFactor“的参数，它说它可以用来定义缩放速率。

因此，我使用了以下代码：

device.videoZoomFactor = device.activeFormat.videoZoomFactorUpscaleThreshold;

但是应用程序崩溃了，并显示“videoZoomFactor超出范围”。这是怎么发生的？我应该怎么做才能使相机变焦？

Answer 1

在下面的代码片段中，它可以正确地为我工作：

if ([device respondsToSelector:@selector(setVideoZoomFactor:)]) {
    if ([ device lockForConfiguration:nil]) {
        float zoomFactor = device.activeFormat.videoZoomFactorUpscaleThreshold;
        [device setVideoZoomFactor:zoomFactor];
        [device unlockForConfiguration];
    }
}

尝试记录device.activeFormat.videoZoomFactorUpscaleThreshold并查看其实际值是什么。

Answer 2

您需要先检查预设，使用- (BOOL)supportsAVCaptureSessionPreset:(NSString *) sessionPreset

此外，device.videoZoomFactor范围应在1.0和2.0之间，因此在进行设置之前，请先检查范围。

Answer 3

// in class
CGFloat zoomBegin;
CGFloat zoomMax;

// on create video connection
NSError *error;
if( YES == [camDevice lockForConfiguration:&error] )
{
    // A maximum zoom factor of 1 indicates no zoom is available.
    zoomMax = camDevice.activeFormat.videoMaxZoomFactor;
    [camDevice unlockForConfiguration];
}
[self.view addGestureRecognizer:[[UIPinchGestureRecognizer alloc] initWithTarget:self action:@selector(pinchToZoom:)]];

- (void)pinchToZoom:(UIPinchGestureRecognizer*)gesture
{
    switch (gesture.state)
    {
        case UIGestureRecognizerStateBegan:
        {
            zoomBegin = camDevice.videoZoomFactor;
            NSLog(@"zoom begin:%.3f", zoomBegin);
        }break;
        case UIGestureRecognizerStateChanged:
        {
            CGFloat zoomTo = zoomBegin + (gesture.scale * 2 - 2);
            // step 0.01 between 1.0 and zoomMax (4x on iPhone 6s)
            int msc = (int)(((zoomTo+0.001)*100))%100;
            zoomTo = (NSInteger)zoomTo + msc * 0.01;
            zoomTo = fmaxf(1, fminf(zoomTo, zoomMax));

            if ( camDevice.videoZoomFactor != zoomTo )
            {
                dispatch_async(sessionQueue, ^{
                    NSError *error;
                    if ( YES == [camDevice lockForConfiguration:&error] )
                    {
                        camDevice.videoZoomFactor = zoomTo;
                        [camDevice unlockForConfiguration];
                        NSLog(@"zoom changed:%.3f", zoomTo);
                    }
                });
            }
        }break;
        default:
            break;
    }
}