To add a video to your KB article, first copy the embed HTML for the video you want to add. 

Then, when composing your article in Groove, click on the source code button in the top right of the article editor. 

Paste the HTML for your video into the source of your article and click OK. 

Your video should now appear in the body of your article. 

And here's what it looks like when it's published on your page.