VLC file conversion issue

[Gosunkugi]

Just a quick question regarding VLC's conversion feature. I've been recording gaming videos with Fraps and due to the high file size (avi), running it through VLC's convert/save option to compress it into a manageable size (mp4), I've noticed with videos over a certain length, 30 minutes or so, I get some audio sync issues.

I'm really happy with the quality otherwise, shrinking a 9 gig video down to 400 meg with no discernible quality loss is ideal for my purposes and normally such a little niggle of half a second sound delay wouldn't bother me, but as I'm uploading to Youtube where every mistake is glaringly obvious for all to see I'd like to clear it up.

Any tips or solutions for fixing this? I've tried altering the bitrate and sample rate to no effect. Is there a specific codec I should be using?

Cheers.