问题
I am researching creating multi-output devices on either OS X or iOS, and I found out that CoreAudio would allow you to create aggregate devices. My first question is, does iOS allow you to do this. I know that this is certainly possible on OS X, but I've heard that iOS will not allow it. I would really appreciate an example of how you would go about detecting multiple audio output devices and creating an aggregate device, all using swift. I have checked here, but it doesn't fully answer my question, and the answer it does have is based on Objective-C. I'd appreciate any help, and thanks in advance!
回答1:
The aggregate audio device API is not publicly available on iOS, so you cannot create those devices yourself.
However iOS will create aggregate devices* for you depending on the most recently attached audio hardware and some other rules if you activate an AVAudioSession that uses the .multiRoute category.
When you get a route change notification due to an audio interface being added or removed, you can create a remote IO audio unit with the right number of channels. I haven’t tried using multi route audio with AVAudioEngine nor have I tried using only a subset of the available channels.
* They’re probably aggregate devices, although you never see them or interact with them directly.
来源：https://stackoverflow.com/questions/38810339/programmatically-create-aggregate-audio-devices-in-swift-using-coreaudio