Flanking and bodychecks

In this endgame it is Black to move. He is fighting for a draw with bishop and king against the pair of white passed pawns (g4,h4). In the game, the pawns outran him. Now it is your turn to try and find the narrow path to safety. Endgame expert GM Dr Karsten Müller has analysed the ending and shows the narrow path to a draw. Can you find it?