A downloaded app for the iPhone has solved the variable frames per second problem! This video is smoother but the focus isn't as good and I haven't synced the sound well. I shall have another go using a gorillapod to hold the iPhone steady. (Again, thanks to steamsounds.org.uk for the sound effects).
Making videos is a great excuse for putting off cutting out the quoins for the chapel (which I have learned is the architectural name for the stone blocks on the outside corner wall of a building).