Liza Foreman Making its world premiere in the main competition at the San Sebastián Festival on Sept. 19, “Il Boemo,” the story of a forgotten Czech composer who rose to fame in the second half of the 18th century, has taken the award-winning filmmaker Petr Václav more than a decade to complete. Known as Il Boemo, Josef Mysliveček’s fame was short-lived. He died before reaching the age of 44, after a whirlwind career composing music for Italian courts and theaters. But Václav, together with his DPs, Diego Romero and Suarez Llanos, costume designer Andrea Cavalletto, and a slew of top operatic singers, has created an action-packed period piece, celebrating his tumultuous life, operatic drama, and the aesthetic beauty of the era.