Apologies for my lack of clarity.

What I am asking is :-

If I download 1 hour of youtube video, how much data is it?

I guess this may be like  "How long is a piece of string?"  - there may be a lot of variables.

I have currently signed up for 20 Gb of download for $25.00.

I have done this as a couple of tech's thought that only 5Gb would be too little.  It would not be good to have a presentation slow down and go jerky [if that's what would happen if we used all our allocation].

We'll try it a few times and see.