Is there any great and free video converting tool?

I know a little about converting file software or file dimensions for the matter, however I paid attention as downloading a television show from two different solutions that a file size was a lot smaller, the mp4, as the other one was a lot bigger, the avi. It was the equal display and there wasn’t much unlikeness in image quality, so I am not familiar with why one download was 60mb as the download from the additional solution was 341 MB! I just would like to find a free of charge transfering video tool what makes a great rate of success of converting existing avi documents to mp4. video converter needs payment, as a result that is not my selection.

Handbrake
http://handbrake.fr/

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