When the Islamic State terror group swept across northern Iraq in 2014, they tried to wipe out the Yazidi people, a minority ethnic group that had lived in the mountains for millennia. Thousands of men were killed, and women and girls forcibly enslaved. The ancient Yazidi culture was at risk of being eradicated. A new project aims to teach young Yazidis the ancient music of their ancestors and create a permanent record of the culture. And as Henry Ridgwell reports from London, the songs are helping the Yazidi to overcome the mental scars of their brutal treatment at the hands of Islamic State.