Bassma Kodmani, Syrian opposition negotiator

After five years of bloodletting and suffering the Syrian war has a new, potentially game-changing dynamic. The combined forces of the Assad regime and its Iranian and Russian backers are pushing back the rebels in the north and west of the country; a mooted truce appears to have been brokered on Russia's terms and seems unlikely to halt the military push. Stephen Sackur speaks to Bassma Kodmani a representative of the so-called moderate rebels - is the only realistic choice in Syria Assad, or Islamic State?