Or......
PAL 4:3 DAR = 16:15
PAL 16:9 DAR = 64:45
NTSC 4:3 DAR = 8:9
NTSC 16:9 DAR = 32:27
EDIT: In February 2006 I conceived a tool called
ARS Calculator to help people work out Aspect Ratio Signalling (ARS) ratios (ie: PAR, SAR, DAR) for use with encoders such x264 and XviD
Cheers