fitting a video to the max width of window

Hi, I have been trying to make a youtube video fit to the maximum width of a window but so far all attempts have failed. The problem I am having is that the video has a black bar on the left and right side. Idk why that is happening but if that is removable than I would like some help with that. And will the fix also work with a normal video file? my website is umi-productions.nl. And the problem I am having is on the landing page(the page where the video is on).