@fsfe First off: congrats on this! It's a very nice rendition of the book and a very pleasant voice to listen to.
Sadly I had to see there are no official captions, asides from Youtube's bad, automated ones.
I started working on them and will most likely be able to finish them later today and MAYBE do a German translation (based on the book) as well.
If you'd like I could, once finished, provide the WebVTT or SRT caption files for you to upload it to the sites, if you want. 🙂