I would like to share you a best converter i have used:
Daniusoft Video Converter for Mac:
Click here to see the full reviews and have a free trial:
http://www.daniusoft.com/video-converter-for-mac.html#161
It can convert almost any the video format to another with high output quality.
This full-featured video converter software also can help you:
1.convert between all mainstream video and audio formats,such as(mp4, mov, m4v, vob, XviD, avi, flv, 3gp, 3g2, mpg,wmv,HD videos,etc; m4v, mp3, wav, ac3,etc)
2.extract audio tracks from video files to other audio formats
3.support all popular portable multimedia players
4.edit video-Effect,Merge, Trim, Crop and Snapshot
Hope it cannot let you down.
I tried a lot of free video converters and select this one at last, Because convert video file with free software is really waste time, it will take you more than 3 hours to convert one movie i think. and many freeware can not afford large files like this. The output quality is not good enough always.