The multimedia file systems uses different paradigm than the traditional file systems.
To access any file, then a process first issues an open system call. On success, the caller is given some kind of token, called as file descriptor in the Unix platform or as handle in Windows platform, to be used in the future calls. At that point, the process can issue a read system call, that provides the token, the buffer address and byte count as parameters.
Now, the OS then returns the requested date in the buffer, and additional read calls can then be made until the process is finished at which time it calls close to close the file and then return its resources.