Where's the legal contract part? If my video is leaked by the other party, I'd like to at least have a clear contract so I can issue takedown notices, sue for copyright damages, etc.
(Edit: Not a new idea, certainly, but well executed so far.)
That would probably be a matter between you and the other party (the video never touches the app's servers). There's nothing stopping you from drawing up a contract yourself, but I don't see any reason for this app to provide something like that.
I'm pretty sure leaking a sex video without consent is already illegal in most countries. And you can sue the other party for a lot more severe crimes than copyright damages.
You might be surprised how much the law lags at criminalizing morally reprehensible acts enabled by technology, like revenge porn.
I can't speak to other countries specifics, but in the US the most effective avenue currently appears to be copyright claims. That's a civil proceeding, so the jilted ex is only on the hook for financial penalties.
(Edit: Not a new idea, certainly, but well executed so far.)