To add a Youtube or Vimeo video to a marketing piece or template, click the "Content" tab on the right, then drag and drop a "Video" content block into your piece where you want it to display.
Click on the newly added "Video" content block, then paste your Youtube or Vimeo video link in the "URL" field on the right. This should pull in the thumbnail image from the video with a play button overlay that you can customize. Please keep in mind that currently this option is only available for YouTube and Vimeo videos.
For videos hosted elsewhere you may want to use an alternative method.
Note: We do not recommend attempting directly embedding a video to play in an email as there can be associated issues (receiving email clients may not display the video, or may block the email entirely).