How to access multiple buffers in UnsafePointer<AudioBufferList> (non-mutable)

问题

I've been trying to use the new AVAudioSinkNode in Core Audio. It passes audioBufferList which is of type UnsafePointer<AudioBufferList> to the closure handling the audio.

The implementation of AudioBufferList in Swift is such that you cannot access multiple buffers, if there are more than one. Apple provided a wrapper for the mutable version, UnsafeMutablePointer<AudioBufferList>, which is called UnsafeMutableAudioBufferListPointer and allows access to multiple buffers.

But I cannot find a relevant wrapper that I could use with the non-mutable UnsafePointer<AudioBufferList>....

let sinkNode = AVAudioSinkNode() { (timestamp, frames, audioBufferList) -> OSStatus in
    // audioBufferList is UnsafePointer<AudioBufferList>
    // how to access multiple buffers in audioBufferList?
}

Thanks in advance!

回答1:

To access each AudioBuffer in an AudioBufferList in Swift, you may choose two ways:

• Do some pointer operations yourself and calculate each address of AudioBuffer.
• Use UnsafeMutableAudioBufferListPointer forcefully.

If you could find a right sample code before UnsafeMutableAudioBufferListPointer was introduced in Swift, the first way might be your option, but as for now, it's hard to find one.

---

To use UnsafeMutableAudioBufferListPointer forcefully, you may need to convert UnsafePointer<AudioBufferList> to UnsafeMutablePointer<AudioBufferList>, which is not too difficult:

            let audioBufferListPtr = UnsafeMutableAudioBufferListPointer(UnsafeMutablePointer(mutating: audioBufferList))

I believe you know how to access buffers once you get UnsafeMutableAudioBufferListPointer.

Caution: Even if type conversion from UnsafePointer<AudioBufferList> to UnsafeMutablePointer<AudioBufferList> is easily made, the actual region passed through audioBufferList is not mutable. You may need extra care not to mutate such region.

来源：https://stackoverflow.com/questions/60801491/how-to-access-multiple-buffers-in-unsafepointeraudiobufferlist-non-mutable