MPEG Streamclip audio problems

I am trying to convert an .avi file to .mp4. I only plan on doing this 1 file so don't plan on spending money for software I'll use just once.
The only free solutions I've found are MPEG Streamclip and iSquint.

After trying iSquint the quality of the converted file was almost unwatchable so then I gave Streamclip a go, but on any setting, default or not, I can't get any audio after the conversion.
The video is very good quality though.
There is other options to export to as well. (see pic)
Seeing as the video is working I tried the 'export audio' option instead, but after clicking it speeds to 100% completed and produces a file (tried for .mp3) with no sound.

btw the avi file plays fine, but I am looking to get it into iTunes somehow.

any suggestions??

Thanks, b.