Xvid driving me mad

hello, i have multiple xvid files i want to convert to dvd. i previously joined divx files to convert with virtualdub which worked great but it wont work for the avi’s cos it says they arent the same file format.

Anyway in converting to dvd using tmpgenc dvd source creator (fairly new) it recognises the 27minute files as almost 70mins meaning i have a lower bitrate and cant fit eveything i want on 1 dvd disk. Anybody know why or what to do?
any help apreciated.