You cannot embed forms and videos directly in email messages. Most email clients will not display or process forms and videos that are added directly to emails. This is not an Envoke limitation, it's a limitation by email technology in genaral.
What you can do instead:
Adding videos to email
Add a link or image and link it to your video page on YouTube, Vimeo or other video hosting service. For the image you could use a screenshot from your video. Adding a play button is recommended.
Adding forms in emails
Link to the web page or landing page that has the form on it.
Read more about adding forms to your website.
Link to the hosted version of your Envoke form. You can get the link to the hosted version by clicking the Preview button on the form editor page.
In addition to links you can also use a button, like this: