In an earlier post I mentioned WorkAudioBook, an app I have used with audio files like the audio from the person on YouTube reading Harry Potter aloud. The app automatically divides the audio into phrases, using the natural pauses of human speech. Here is a screenshot:

You can then listen to the one phrase repeated over and over or let the app continuously play the audio, go to the next phrase, go to the previous phrase, etc., etc. It has features for using subtitles or a transcript but I don't have subtitles or a transcript for these YouTube recordings so I haven't used those features. I am listening to this recording with speed reduced by 20%.

I am simply unable to make sense of the recording as it is on YouTube. The person reads very quickly. This app makes it very convenient for me to be able to focus on one spoken phrase at a time.

It has a free Windows version at http://workaudiobook.com/ There is an Android version (In-app purchases, not expensive) at https://play.google.com/store/apps/details?id=com.povalyaev.WorkAudioBook . The app has not been updated recently. I have not had any problems with it.

Maybe someone here could try out the subtitle/transcript features and tell us how well they work.