The present invention is directed to an application programming interface. More specifically, the present invention relates to an application programming interface designed for handling interaction between an audio/video controller and an audio/video file system. In one exemplary embodiment, the application programming interface includes a number of function calls which direct the audio/video file system to perform a variety of functions. In addition, the application programming interface permits devices capable of handling different types of data, such as isochronous and asynchronous data, to communicate with the audio/video file system.