objective-c record audio session output

Question

I am writing an app that generates music. I am using OpenAL to: modify gain; modify pitch; mix audio; and play the resulting audio. I now need to record the audio as it is being played. I understand that OpenAL does not let you record the output audio. The other options I have found is to use audio units. However because I need to mix/pitch/gain the audio and record it, it seems I need to write all the audio processing so I can have access to the output buffer. Is this correct? Or is there a different iOS API I can use to do this. If not then is there a 3rd party solution already that lets me record the output (paid solutions are fine)?

Answer 1

You are correct.

Audio Units are the only iOS public API that allows an app to both process and then record audio.

Trying to record the OpenAL output may well be a violation of Apple's rules against using non-public APIs.

The alternative may be to completely rewrite the portions of OpenAL you need (there may be open source for some portions) running on top of the RemoteIO Audio Unit.

Answer 2

The best way to go is likely to be Core Audio, since it will give you as much flexibility as you need. Take a look into the Extended Audio File Services reference pages.

Using and extended audio file you should be able to set up a file format and audio stream buffer to send the final mixed output to, and then use the ExtAudioFileWrite() function to write the samples to the file.