no sync in video ipod

hi folks .. bought a new ipod last week..
i use free ipo video convert to venvert files
to mp4 at res of 320x240 at 1500 bit rate
and audio 160 bps..
but when i play that in my ipod there wont be syncronized audio to the video
.. video appears to be a bit slow than audio..
so what do i do now?