Loading & Selecting audio files into Audio Units

I'm trying to 开发者_StackOverflow社区build a Render Callback function that will load a variety of short sound files, and (according to my custom logic) put them in my mixer Unit's iOData audioBufferList. How do I load an aif or caf file into the program, and appropriately import its samples into the ioData?

See Extended Audio File Services Reference, particularly "ExtAudioFileOpenURL" and "ExtAudioFileRead". Remember not to do anything too time consuming in the render callback (e.g. opening a file may be considered time consuming, allocating memory definitely is).