Saving an audio file in documents directory

Question

I am selecting an audio file using MPMediaPickerController, once I select, I want it to store into my application sandbox (some where in documents directory). Is there any way to do so?

//I am implementing MPMediaPickerController delegates

- (void)mediaPicker:(MPMediaPickerController *)mediaPicker didPickMediaItems:(MPMediaItemCollection *)mediaItemCollection
{
    //Here I can store selected audio into my application sandbox, but don't know how?

    NSLog(@"%@",[mediaItemCollection description]);
}