I am planning to put a video there :)
I just want to figure out what the service is about and whether it's worth my time as soon as possible so I can bounce / explore further.
So IMO the screenshot would be much better and less expensive / difficult for you to produce!
Maybe I am not getting what your app is about after all...
Nowadays they get a link in some cloud storage send it via email that you loose it and if you want to add one more person into the discussion it becomes messy. Or they use FB chat that doesn't work in many cases. etc.