From UnsafePointer<UnsafePointer<CFloat>> to an array of floats in Swift?

问题

I'm trying to access AVAudioPCMBuffer.floatChannelData using Swift but it is of type UnsafePointer<UnsafePointer<CFloat>> (in Objective-C, @property(nonatomic, readonly) float *const *floatChannelData) and any attempt I make to access it results in execution failed.

Sample code to set-up a quick AVAudioPCMBuffer in a Swift Playground is included in a previous question:

Getting AVAudioPCMBuffer working (AVAudioFile.mm error code -50)

回答1:

Does this work?

let channels = UnsafeBufferPointer(start: myAudioBuffer.floatChannelData, count: Int(myAudioBuffer.format.channelCount))
let floats = UnsafeBufferPointer(start: channels[0], count: Int(myAudioBuffer.frameLength))

回答2:

What you can also do is in order to access AVAudioBuffer:

for var i = 0; i < Int(audioBuffer.frameLength); i+=Int(audioMixerNode.outputFormatForBus(0).channelCount) {
    self.audioBuffer.floatChannelData.memory[i] = 0.0f; // or whatever
}

You can find more about that in the Apple pre-release documentation:

The floatChannelData property returns pointers to the buffer’s audio samples, if the buffer’s format is 32-bit float. It returns nil if it is another format. The returned pointer is to format.channelCount pointers to float. Each of these pointers is to frameLength valid samples, which are spaced by stride samples.

来源：https://stackoverflow.com/questions/24090119/from-unsafepointerunsafepointercfloat-to-an-array-of-floats-in-swift