Ukrainian war correspondent Mstyslav Chernov has been described as one of the best documentary filmmakers of our time. He risked his life to film the lives of others during the Russian siege of Mariupol in 2022. His award-winning documentary "20 days in Mariupol" has just been nominated for an Oscar. He spoke to FRANCE 24's Gavin Lee about what the nomination means to him, the importance of making a lasting record of the tragedy of Mariupol and how journalists' work has become so dangerous.