Videos can be displayed on your slides, linked from the following platforms: Youtube, Vimeo, and Wistia.
In both, the Outline and Design Section, you can click on Add Content Block and select Video. You'll get the slot to paste your video URL link, from the platforms mentioned above.
A preview of your video will display.
Keep in mind while you present, when you get to the video slide it will automatically play in full screen. Therefore, you can't have more content blocks on the slide where you added a video.