Wow this sounds so scary. The loud sound was from the canon. It is part of the 21 gun salute as a respect for the arrival of the president. The canon was fired when the president arrived at the celebration of NDP. But since this is not the real NDP celebration, so a stand in for the president was arranged.
Each time the canon fired, I would startled ...lol . That's the reason why my camera moved when I was videoing.