Hi Peter,
It's just south of Heads of the Valleys, east of Merthyr Tydfil. It's not really my area as I'm based in Brecon but the conditions have been better here lately and it's a really easy place to flop out of the car and into the air from. You're also likely to bump into others here when the conditions are right, on the evening of the video there was a powered hang glider and two paramotors flying from there. A lot of ridge soaring goes on about a mile away. I didn't know about the place until recently as I have no interest in the valley areas (run down towns with bored kids, burned out cars in laybys, etc.) but it turns out to be a bit of a pilot's mecca.
I've attached a map, the red area shows good launching areas. Beware of low flying police helicopters which seem to show up regularly.
Cheers
Steve.