Automatically Pause When Visiting Youtube URL

I was tasked to capture the image on a specific time when visiting youtube. So far I haven't got any success using chromium. For example, i need to capture the image of a video exactly after 180 seconds, i will have to visit this URL https://www.youtube.com/watch?v=Biagyb7AcK8&t=180s , what i did is to issue pause command OnChromiumLoadEnd but it fails depending on internet speed.. Are there any command to make video is paused on a specific time?

EDIT here is my code OnChromiumLoadEnd:

begin
  CEFWindowParent1.SetFocus;
  Sleep(200);
  keybd_event(Ord('K'), 0, 0, 0);
end;