NSSpeechSynthesizer startSpeakingString:toURL: doesn't work on long texts

An utterance can control speech parameters, you can split text into sections, create an utterance with each section and call speak for each utterance in the SpeechSynthesizer.

import UIKit
import AVFoundation

class ViewController: UIViewController {
    
    var synthesizer : AVSpeechSynthesizer!
    
    
    func speak(utterance: AVSpeechUtterance){
        print("\(type(of: self)) \(#function)")
        synthesizer.speak(utterance)
    }
    
    func utteranceWith(_ string: String) -> AVSpeechUtterance{
        let utterance = AVSpeechUtterance(string: string)
        utterance.voice = AVSpeechSynthesisVoice(language: "en-GB")
        return utterance
    }
    
    
    override func viewDidLoad() {
        super.viewDidLoad()
        synthesizer = AVSpeechSynthesizer()
        synthesizer.pauseSpeaking(at: .word)
        
        guard let filepath = Bundle.main.path(forResource: "book", ofType: "txt") else { fatalError("Can not get filepath") }
        
        
        do {
            let contents = try String(contentsOfFile: filepath)
            let paragraphs = contents.components(separatedBy: "\n")
            for phrase in paragraphs {
                speak(utterance:utteranceWith(phrase))
            }
        }
        catch {
            print("Contents could not be loaded.")
        }
    }
}