DV capture - A\V out of sync

im capturing from a DV to PC using S-video port on capture card but viode starts to get gradually out of sync after abt 30 min of clip...could capturing rom firewire instead of s-video wopuld fix this problem??

im new to video and DV capture, dont know much abt

searching on the net revealed that capture through firewire shouldnt have any synbc problems but there wasnt any clear answer