How videocapture works to grab images

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Hello,

In my program I need to minimize the delta between the image acquisition and the process time. In other language when I want to grab an image if there is a image taked 20 ms ago or 30 ms later I prefer to grab the image 20 ms ago.

So here is my question how videocapture works. Is there a circular buffer and when we want to grab an image it send us the last in the pipe. Or when we want an other image the videocapture just wait for the next image from the camera ?

I don't find any information about the videocapture way of working.

Can someone give me answer about it?