Clunk Clunk noise?

Hi, a friend of mine has sent me this video asking if I can have a look at his son’s bike. Now, I am no bike expert at all, but I do have tools, a stand and a willingness to identify and resolve problems.

Before I get home from holiday and have a look at this bike, do any of you have any thoughts on what it could be?

I can’t tell from the video if it’s coming from the rear hub or the BB or anything. I can’t even identify if it’s during a certain position of the crank stroke…

I’m happy to try to isolate the sound when I’m home but you legends have helped me out before so I’m hoping you can give me some guidance now.

Thanks!!!