Can compressor 4 convert rmvb or mkv to other formats?

Hey there,

I was wondering it is possible to use compressor to convert rmvb or mkv files into mp4 or other formats that FCPX can read? I was trying to convert a rmvb file into some kind of format that final cut pro x can read, but all the files are grey(cannot be selected or added) when I click "add file" button of compressor. Could anyone help me out of this ? Thank you in advance.

Ben Xu