Core Media basics, understanding CMSampleBuffer, CMBlockBuffer and CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer

So, I'm trying to learn basics of Core Media since I need to process real time audio samples in my app. For now I know that I need to configure an AVCaptureSession setting an AVCaptureDevice used to acquire samples and an AVCaptureDataOutput that processes the input from the device and "notifies" an AVCaptureAudioDataSampleBufferDelegate through a captureOutput(...) method.

Now, this one method gets passed the samples as an CMSampleBuffer object, that according to Apple's CM documentation, will contain zero or more media (audio in my case) samples and a CMBlockBuffer, that is

[...] a CFType object that represents a contiguous range of data offsets [...] across a possibly noncontiguous memory region.

OK So this is kinda getting confusing. I'm not a native speaker and I'm struggling to understand what this is supposed to mean. Why do I need this to access my samples? Aren't they stored as an array of raw binary data (therefore homogeneous and contiguous)? I guess this is related to how the underlying memory is managed by Core Media but I can't figure it out.

Also the last batch of samples gets accessed through this CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer  method which expects an unsafe mutable pointer to an AudioBufferList and one to an optional CMBlockBuffer. The first one will be filled with pointers into the latter, and then I may (or may not) be able to access the samples through myAudioBufferList.mBuffers.mData, which might be nil.

Example code from Apple Developers code snippets:

public func captureOutput(_ output: AVCaptureOutput,
                              didOutput sampleBuffer: CMSampleBuffer,
                              from connection: AVCaptureConnection) {

        var audioBufferList = AudioBufferList()
        var blockBuffer: CMBlockBuffer?
  
        CMSampleBufferGetAudioBufferListWithRetainedBlockBuffer(
            sampleBuffer,
            bufferListSizeNeededOut: nil,
            bufferListOut: &audioBufferList,
            bufferListSize: MemoryLayout.stride(ofValue: audioBufferList),
            blockBufferAllocator: nil,
            blockBufferMemoryAllocator: nil,
            flags: kCMSampleBufferFlag_AudioBufferList_Assure16ByteAlignment,
            blockBufferOut: &blockBuffer)
        
        guard let data = audioBufferList.mBuffers.mData else {
            return
        }

}

What's the memory model (or pipeline) behind this? I truly appreciate any help.