Free MKV to MP4 Converter

I have a client that needs to convert MKV and MP4 video files. This project is for a piece of software that converts .MKV video files to .MP4 video format and MP4 to MKV. Requirements for the software: -Must work on ALL Windows operating systems including XP, Vista, Win7 and Win 8 for both x86 and x64bit -Buttons at the top of the program: Add File | Add Folder | Remove | Remove All | Convert | About -Add File - opens up file browser for user to add MKV/MP4 file -Add Folder - open up file browser for user to add entire folder directory -Removee - when user highlights MKV/MP4 file in the display menu, he or she can click Remove to remove the MKV video file -Remove All - removes all mkv files in the file manager -Convert - begins conversion of video files then pop-up status bar begins to display until conversion is done with timer/estimation of how long files will - -- take to convert -About - pop-up diaglog box that includes -Users can drag and drop MKV/MP4 files into file manager view -Screenshot includes a concept but DO NOT use the same icons. Icons must be transparent. -Please thoroughly test the software