Mitchell's Abrasive Emery Cords No. 55, 200 Grit, 0.018" X 50 Ft.

Ok, that video was useless. If you break a different string each time, It's your picking technique. If you keep breaking the same string in the same place, it has something to do with that place. If the D string is breaking at the saddle every time, there is probably a burr on that saddle. Try taking the saddle off and using some abrasive cord on the grove where the string will sit.