Any video converter question?

Ok so my smc isn’t converting either since i had to format my player and reinstall firmware on it, twice and now i dl-ed the new smc and i cant convert videos on it cause it just freezes. But how do i use any video converter, and copy mp4 files to my sansa cause it sais unsupported file format?

Sansa plyaer (at least my e280) only supports .MOV video files