Most email clients do not support video content within the body of an email, and many will actually remove the code for the video altogether. We highly recommend that you do not attempt to embed a video within your email, as this can cause several unforeseen issues. While you cannot add a video to the email, there is a workaround that you can follow.
What you will need to do is add an image placeholder (typically with a play button overlayed on it) into your Core iQ email. Then you will want to link that image to a hosted version of your playable video. You can host this video on your website, or a platform like YouTube or Vimeo. This allows you to link the video without actually placing it into your email body. When a recipient clicks on the video image, they will be brought to your video.