Sharing videos with your subscribers is a great way to engage them. You can use Vimeo to host your videos and embed them in your posts, and Buttondown makes it easy to drop those links right into your newsletter.
In the email version of your newsletter, Buttondown will render that video as a thumbnail with a play button. When your subscribers click on the thumbnail, they'll be taken to the video on Vimeo.
On the web, Buttondown will render the video as an iframe. This means that the video will play inline in your newsletter, and your subscribers won't have to leave your site to watch it.