I always use MKVtoolnix (in Windows) to join 2 or more mkv files. It's a simple process, very fast, and no files converting. I thought MP4Tool will do the same (because the name is similar) but no. There's a join button but it's always greyed out. All I want is a simple tool to join 2 or more MP4 files without converting. Free is preferable. Mac "or" PC. I tried Free Video Joiner on Windows. It's very slow and it converted the files. I also tried Avidemux but it's crashed. Any helps is appreciated.