Can you post how you do it for images? Maybe it will give us some ideas on how to help you. Not to mention, it would probably help a lot of people too. 

Or maybe describe why you want dynamic videos? Use cases? Thanks! 

Hi! I just put together a script that can do this for you - https://gist.github.com/RobertCam/3b74c7098667f0a3ef24ca576891eb52

I’ve got a landing page with instructions on setting it up as well - http://unbouncepages.com/video-swap/

Let me know if this is useful and maybe your use case. If more people could use it we might add it to the list of workarounds.

This is an interesting concept and great solution, Robert!