Hi ThePhantomUpvoter ,
I don't know why you are directly giving path of video file to WebBrowser control?
Instead of that you can prepare a html page with video tag and width , height and source attribute specified for it.
Then give this html page's path as Url to your WebBrowser control. Try this whether it is working or not?
Something like this
webBrowser1.Url = new Uri( @"D:\myfolder\MyHtmlPage.html");
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Thnaks