A failed attempt at four channel audio output for the iPadPro using Swift 2 / CoreAudio (3rd and 4th channels are discarded).

It’s an interesting example because it shows how to:

• output realtime, procedural audio using a CoreAudio kAudioUnitSubType_RemoteIO audio unit.
• cast between self and UnsafeMutablePointer<Void>
• implement a c callback via AURenderCallback
• cast AudioBufferList AudioBuffer to a swift array without accidentally copying (UnsafeMutableBufferPointer<Float>)

API calls: AudioComponentFindNext, AudioUnitSetProperty, AudioUnitInitialize, AudioOutputUnitStart

Structs/Classes: AudioComponentDescription, AURenderCallbackStruct, AudioStreamBasicDescription, AVAudioSession

Constants: kAudioFormatLinearPCM, kLinearPCMFormatFlagIsFloat, kAudioUnitProperty_StreamFormat, AVAudioSessionCategoryPlayback