Snap shot is not working?

问题

I am new to mobile programming. I am working in H264 video rendering in iOS application using VideoToolBox framework. It has one feature to take snapshot while rendering the video. Whenever I take a snapshot, I get the Black screen only. I tried this 1. renderInContext, 2. drawViewHierarchyInRect, 3. snapshotViewAfterScreenUpdates method to capture the rendering the video but returns a Black screen only.

//snapshot coding
UIGraphicsBeginImageContextWithOptions (self.view.bounds.size, YES, 0.0);
[self.view.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *snapshotImage = UIGraphicsGetImageFromCurrentImageContext();
mImageView.image = snapshotImage;
UIGraphicsEndImageContext();
UIImageWriteToSavedPhotosAlbum(snapshotImage,self, @selector(image:didFinishSavingWithError: contextInfo:), nil);

回答1:

Check this out, following chunk of code works for me to take screen's snap shot

if ([[UIScreen mainScreen] respondsToSelector:@selector(scale)])
    UIGraphicsBeginImageContextWithOptions(APP_DELEGATE.window.bounds.size, NO, [[UIScreen mainScreen] scale]);
else
    UIGraphicsBeginImageContext(APP_DELEGATE.window.bounds.size);

[APP_DELEGATE.window.layer renderInContext:UIGraphicsGetCurrentContext()];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
UIGraphicsEndImageContext();
NSData * data = UIImagePNGRepresentation(image);

I guess, it will help you. let me know if so

回答2:

I've not worked with video yet, but a simple snapshot of UIView with subViews on it works fine

+ (UIImage *)makeSnapShot:(UIView *)view image:(UIImageView *)imageView
{
    CGFloat offset_x = /*your_value*/;
    CGFloat offset_y = /*your_value*/;
    UIGraphicsBeginImageContext(view.bounds.size);
    [view.layer renderInContext:UIGraphicsGetCurrentContext()];

    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();

    CGRect rect = CGRectMake(offset_x, offset_y, imageView.bounds.size.width, imageView.bounds.size.height);

    CGImageRef imageRef = CGImageCreateWithImageInRect([image CGImage], rect);
    image = [UIImage imageWithCGImage:imageRef];
    CGImageRelease(imageRef);

    return image;
}

回答3:

Not sure if this is what you're looking for, but if you need to get a snapshot of the VTDecompressionSession, you can send the CVImageBuffer that you get from the decodeFrame callback into this method to get a UIImage. You can also add your CIContext to the parameters list instead of using the temporaryContext.

+ (UIImage *) UIImageFromCVImageBufferRef:(CVImageBufferRef)imageBuf
{
    CIImage *ciImage = [CIImage imageWithCVPixelBuffer:imageBuf];
    CIContext *temporaryContext = [CIContext contextWithOptions:nil];
    CGImageRef videoImage = [temporaryContext
                             createCGImage:ciImage
                             fromRect:CGRectMake(0, 0,
                                                 CVPixelBufferGetWidth(imageBuf),
                                                 CVPixelBufferGetHeight(imageBuf))];
    UIImage *image = [[UIImage alloc] initWithCGImage:videoImage];
    CGImageRelease(videoImage);
    return image;
}

回答4:

func takeScreenshot(_ shouldSave: Bool = true) {
       var screenshotImage :UIImage?
       let layer = UIApplication.shared.keyWindow!.layer
       let scale = UIScreen.main.scale
       UIGraphicsBeginImageContextWithOptions(layer.frame.size, false, scale)
    self.view.drawHierarchy(in: self.view.bounds, afterScreenUpdates: true)
       screenshotImage = UIGraphicsGetImageFromCurrentImageContext()
       UIGraphicsEndImageContext()
       if let image = screenshotImage, shouldSave {
           UIImageWriteToSavedPhotosAlbum(image, nil, nil, nil)
       }
   }

来源：https://stackoverflow.com/questions/27646689/snap-shot-is-not-working

标签

ios

objective-c

xcode

snapshot