How to decompress video files MPEG-2 ,MPEG-4 or any other format.

Hi everyone,

I was asked to do a program which requires to decompress video files of types .mpeg, .m2v, .m1v and .avi.

I wanted to know if there is a form to decompress any of this formats in a single program and how could it be done. We want to decompress them so we can analyze how does the DCT and other compressing procedures work. Thanks to all of you in advance!