I use the new method that writes a speech utterance to file:

func write(AVSpeechUtterance, toBufferCallback: AVSpeechSynthesizer.BufferCallback)

And judging whether the write has ended by whether the buffer length is 0.

synthesis.write(utterance) { (buffer) in
   guard let pcmBuffer = buffer as? AVAudioPCMBuffer else {
        log("unknow buffer type: (buffer)")
         return
   }
   if pcmBuffer.frameLength == 0 {
       print("Finished")
       self.writeComplete()
   }
   else {
      self.writeToFile(buffer: pcmBuffer)
   }
}

It works well on iOS 16 and early,but on iOS 17(my device is 17.2.1), no pcmBuffer callback whose frameLength is 0,so i cant know write is complete,causing my writeComplete` method never to be called.

Is there a better (or more accurate) way to determine write completion?