It's easy to add videos from Google Drive. First, add the Embed gadget by dragging it into your content.
Second, go to Google Drive and double click on your video to expand it for playback. Click the "..." icon in the top right, then select "Share".
Finally, copy the Google share code and paste it in the Embed gadget text field. Delete the "view?usp=sharing" snippet at the end of the share url and replace it with "preview", as shown in the video.