I converted a wmv to xvid and did the same for the audio (wma to mp3). Both video and audio came out the same length (30:00) but the audio is out of synch. Then I adjusted the audio and it was in-synch at the beginning but still out-of-synch thereafter. Why is it out-of-synch if it is the same length as the video?

To encode the video I imported the video using directshowsource("C\filename", fps=30, audio=false). Then I converted wma->wav->mp3 (CBR) using BSweet. I used virtualdub, too.