mproj to mp4 conversion is most likely searched by users looking for a way to export .mproj files from iMovie to Windows to MP4 format, something that is only doable with the original software only (you can download it for free). The software supports several formats, for example, including MP4. The free copy leaves a watermark on the video, though.
Old tools called Mine-imator also used .mproj files, but they allowed only export to AVI format and you had to convert them to .mp4 format manually.