I thought it was the hallmark of a good piper to not have any “rhythm” at all on the bellows! My understanding has always been that you pump only when you need a bellows-full of air, with no connection to what’s going on with the tune. In Ennis’s case, with his famously leaky set, he seems to have been pumping almost nonstop. Maire Ni Ghrada pumps like that too, although I assume that’s just a habit as I doubt her Wooff set is leaky 
Right…there’s not suppose to be any connection between the rhythm of the tune and the rhythm of the bellows. He definitely stops pumping every so often. The bag can’t be that full, esp if it’s a leaky one. He does do a lot of things with that right arm though, and sometimes comes back pumping pretty fast to (probably) make up for the loss. Just guessing. Who knows, maybe he’s letting his arm rest.
This Video is a gem of piping which should be the subject of study for the aspiring pipers. I must learn this tune…I will do it by ear but if anyone has transcribed this in abc or sheet music (for reference only NOT TO LEARN from)please post for us…I want the Ennis version of this tune.
Thanks in advance… 
Hauntingly beautiful…study the fingers ..amazing…I have videotaped a majority of my pipe lessons with David Power..for the last two or more years he will be leaving but I have a treasure left behind to work on…its all fingers but its cracken great piping…You never really understand tone and sound until you get the breakdown on the fingers etc…
Anyone know when this piece was recorded? What was the programme?
BTW, who posted it to YouTube?