mp4 lipsync problems

[gingerneil]

I am using the following in the latest version tp convert to ipod mp4
<Conversion name="Video Ipod" cmd="-y -i {SOURCE_FILE} -title {TITLE_SUBTITLE} -f mp4 -vcodec mpeg4 -b 1200k -s 640X480 -r 15 {DEST_FILE}" targetExtension=".mp4" />

However, I am getting large lipsync issues - being out by LOTS (ie 20 seconds) by the end of a 1.30 programme.
Any thoughts on how to solve this ?

[gingerneil]

After lots of digging, reading ffmpeg guides and playing about, I am now using the following for Ipod Video conversion:
<Conversion name="Video Ipod" cmd="-y -i {SOURCE_FILE} -title {TITLE_SUBTITLE} -f mp4 -vcodec mpeg4 -b 1200k -s 640X480 -acodec aac -ab 128k -r 15 -async 128000 {DEST_FILE}" targetExtension=".mp4" />

This has now done the trick, and everything seems to be lined up properly.