Play an audio file using RemoteIO and Audio Unit

Question

I am looking at Apple's 'aurioTouch' example for the iPhone and I would like to play an mp3 or wav instead of using the built in mic. I am very new to the audio portion of iPhone programming, but I think I need to modify the SetupRemoteIO(...) function and replace the AudioComponent named 'comp' with a custom AudioComponent that plays a file. Basically I want the app to function exactly the same as the original, but with an audio file as the input instead of the mic.

Answer 1

You just need to convert your audio file to pcm data and then feed that data to the RemoteIO interface during the playback callback.

To read your audio file in, you will want to use ExtAudioFileOpenURL and ExtAudioFileRead. Also make sure to set your audio format with ExtAudioFileSetProperty to convert to your target pcm format (which should be packed, signed integer PCM data).

Playback simply involves responding to the RemoteIO callback (which should be identical to aurioTouch's example) and feeding it the PCM data you loaded up.

The only other tricky part is that loading an entire mp3 file as PCM can take up a ton of memory. You might have to write a loading thread so that you can stay under your memory requirements by only loading your relevant chunk of the mp3.