We do not currently offer the ability to embed videos directly onto your forms.
Alternatively, you can use a Content field on your form to add links to other websites, like YouTube. Simply add a Content field to your form, and select the Insert/edit link option from the formatting toolbar. In the dialog that appears, you can include your video link, display text, and choose whether the video will appear in the current window or a new window.
Learn more about using Content fields in our help guide.