CODEWITHSUNDEEP
swiftcore-audio
akuz
akuz

Reputation: 637

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

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!

Upvotes: 0

Views: 507

Answers (1)

OOPer
OOPer

Reputation: 47876

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.

Upvotes: 2

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