Data usage of network camera

I just got a Tenvis TH661 network camera which works rather brilliantly with my iPhone to let me remotely view my house and garden (I don't need to - it's a fun toy!).
My question is about how these things handle data.
Does the camera upload its video stream on demand (ie only when I use the app to view it), or continuously (using up data upload capacity all the time)?

The first would seem logical but I have no clue how this stuff works. I presume the app needs a server to tell it what dynamic IP my computer has, so maybe data goes through that server?

My guess would be the former. The point may be explained in the product manual, and you router may display the number of bytes sent which would help you to work out the answer.