Video Converter

In my Apple MacBookPro I use the program "iMovie '11" Versione 9.0.4 (16349)

My video files in format .mpg are ignored for inserting into the library. Only files .mp4 will be accepted.

Now I am searching for a "Video Converter" but i didn't find one.

Please show me the way for downloading such a "Video Converter".

Ciao de Eberhard