There is a great piece of freeware called MKVToolNix which lets you merge and convert MKV files. Do you have two or more .MKV files you want to merge? This is perfect for that. Do you have a .AVI file you want to convert to a .MKV file? This is also perfect for that. As the world of entertainment moves into HD and x264 this little application will be very handy. It works under all major windows operating systems, Windows XP x32, Windows Vista x32, Windows Vista x64, Windows 7 x32, and Windows 7 x64.