You have two options to embed a video in your form. We'll outline both below:
Add video to form description
This is the recommended option and can be used for both creating and editing records.
Navigate to your form's Header & Footer section, turn on Form Description and look for the icon in the toolbar that resembles film (next to the image icon):
This will allow you to add an embed URL from YouTube or Vimeo.
Embed URLs for videos are not the same as the regular watch URLs. Please go to the video's share menu and look for the embed option to get the embed URL. For YouTube, these URLs start with https://www.youtube.com/embed
Use a formula field
This option will only work when editing existing records, or after the first save occurred when using Save & Continue mode.
You can use a formula field to embed a video in your form. To achieve this, you first need to enable HTML rendering for your formula field: go to the Advanced section of the formula field's settings and turn on the Render this field as HTML code toggle.
In the formula field itself (on Airtable), include the HTML embed code for your video. Please note that this is NOT just the video's link. Each video platform (e.g. Youtube or Vimeo) will have its own way of providing you with an embed code, but generally speaking you'll find this in a Share menu or similar. Once you've found the embed code for your video, copy the entire code and paste it into your formula field within quotation marks. If your embed code contains double quotes, use single quotes to wrap the embed code in the formula, or vice versa.
Usually, the embed code will also contain settings for the video player, like autoplay, or playback controls. You can modify those settings in the embed code to your liking!
You can set the height allocated for the rendered HTML by setting an HTML Container Height.