Hello Christoffer,
Thanks for writing in! Actually, resizing the browser window is not the correct way of testing it. Be advised that when the video was loaded by the browser, the browser uses your computer resources in rendering the page contents, graphics, and videos. By resizing the browser window, the page elements, contents, graphics, or videos need to be rendered again by the browser to be able to see that those elements are displayed properly. In most cases, it takes time for the browser to rerender the page. This is why you will see first that the video does not follow the browser width right after you resize the browser window. After a few moments, the video gets displayed properly again displaying with the same width of the browser window. This delay is how the browser rerenders the page. It may vary from computer to computer. If you have a less powerful computer, the delay may take longer. When using a gaming laptop or a more powerful computer, you won’t be seeing any difference as you resize the browser window.
Hope this explains it briefly.