RE: Marketing page with form and video revealing only after form submission
                     
                    
                      
                        Hi Marianna,
It can be achieved with extending marketing forms using code.
As we know, the videos have their own Video embed code. 

It can be inserted into the HTML code of the Marketing Page and an id can be assigned to it.
Here, for example, I inserted it after the marketing form.

Then add some script to control the visibility of the iFrame according to the above documentation.
The code snippet is something like:
After going live the page, you can see the following effect when you open the page.

And after submitting, it will be shown as:

You can also continue to optimize your page according to this effect.
By sharing a URL for the form and video, you won't have the problem of seeing the video without submitting the form after forwarding.