根据视频帧的宽高比调整预览图层的大小

Question

我正在尝试对连接到系统的设备进行iOS屏幕录制。我有一个NSView，它包含AVCaptureView类型的videoView。我在videoView中添加了一个sublayer（previewLayer），它显示了视频帧的预览。我试图根据从iOS屏幕录制得到的视频的第一帧大小来保持previewLayer和videoView的宽高比

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＆＃13;

- (void)captureOutput:(AVCaptureFileOutput*)captureOutput didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer fromConnection:(AVCaptureConnection*)connection
{
    CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
    if(imageBuffer != NULL)
    {
        CGSize imageSize = CVImageBufferGetDisplaySize(imageBuffer);
        NSLog(@"imageSize = %@", NSStringFromSize(imageSize));
        CGRect bounds = CGRectZero;
        bounds.size = imageSize;
        CGRect superViewBounds = streamingView.bounds;
         NSLog(@"superViewBounds = %@", NSStringFromRect(superViewBounds));
        if(bounds.size.width>superViewBounds.size.width || bounds.size.height>superViewBounds.size.height)
        {
            CGFloat ratio_width = bounds.size.width/superViewBounds.size.width;
            CGFloat ratio_height = bounds.size.height/superViewBounds.size.height;
            CGFloat ratio;
            if (ratio_width > ratio_height)
            {
                ratio = ratio_width;
            }
            else
            {
                ratio = ratio_height;
            }
            bounds.size.width = bounds.size.width/ratio;
            bounds.size.height = bounds.size.height/ratio;
            bounds.origin.x = CGRectGetMidX(superViewBounds)-CGRectGetMidX(bounds);
            bounds.origin.y = CGRectGetMidY(superViewBounds)-CGRectGetMidY(bounds);
            NSLog(@"bounds calculation = %@", NSStringFromRect(bounds));
        }
        [self.previewLayer setFrame:bounds];
         NSLog(@"preview layer = %@", NSStringFromRect(self.previewLayer.frame));
        self.previewLayer.videoGravity = AVLayerVideoGravityResizeAspect;
        [self.previewLayer setBackgroundColor:CGColorGetConstantColor(kCGColorWhite)];
        [_videoView setFrame:bounds];
    }
}

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输出

图像1 - 在纵向模式下第一次加载视图时 图2 - 当iOS设备方向更改为横向模式时 图3 - 当iOS设备朝向纵向模式时

如果设备保持原样而不改变方向 我得到以下日志

CoreAnimation：警告，删除线程与未提交的CATransaction;在环境中设置CA_DEBUG_TRANSACTIONS = 1以记录回溯。

然后在更改设备的方向时，它显示如下