The size parameter is the size of the elements, not the size of the
data. The size parameter should be 1, and the elements should be the
number of bytes.
The reason why I'm making this change is because the fread/fwrite would
fail when the parameters were swapped.
This adds functions for piping a command line program's stdin or stdout.
Note however that this is unidirectional only.
This will be especially useful later on when implementing MP4 output,
because MP4 output has to be piped to prevent unexpected program
termination from corrupting the file.