Embedding a video in an email is not possible in any email provider or delivery platform.
That said, we are happy to offer a little trick that we here at Remarkety use which may help:
1. Upload the video to Youtube or your preferred site
2. Take a screenshot of the first frame
3. Upload image to your campaign and
4. Add a link to the page with the full video url. See how to add the video url:
Here is an example of how this looks in an email sent to a Gmail account: