All file IO in mel requires the use of fopen and fclose to open and close files on the hard drive. When writing binary data we need to use fwrite. There are a few small issues you should be aware of, firstly mel is a high level language so you don't get the low level control you need over the binary data. For example, it is impossible to write a 4 byte float to the file since all floats in mel are stored as 8byte doubles.