Nero Recode, no sound

I’m trying to convert some .avi files to .mp4 files for my iPod. Whenever I try to play them in any media player or try to convert them, there’s no sound. Anybody know how I can fix this? Thanks.

Okay, I installed an AC3 codec and ran regsvr32 /u “C:\Program Files\Common Files\Ahead\DSFilter”, then tried playing the files in Nero Showtime. They work fine there. For some reason, I still can’t get sound in the preview in Nero Recode. Any ideas?