I need a free program that will convert .Xvid files to .mp4 files so that it will be playable on an ipod.

.Xvid files generally come with good video quality so I need the software to preserve the picture quality and sound quality.

Please give a list of softwares you had used or one you would strongly recommend. (No trials please - I HATE softwares that claim to have a 'tiral' period and only converts only a percentage of the video.)