Or, an NVDA-addon that someone wrote! Here's the link:
https://cloud61.de/index.php/s/TBnTN3T8X2KCQ3mAnd here's how it works. Just place yourself in your browser on a YouTube video. Then, you can use NVDA + y to convert to mp3, and NVDA + shift + y to download as mp4. NVDA + control + y opens the folder where the downloaded videos are saved, and that keystroke works from anywhere of course. You can't set the location yet, but if you can open the folder with the above mentioned keystroke, you just move it to where you want to have it. I think that's so cool, since it's just one keystroke! And then just open the folder and move it, but that's it! I used Elten before, and that was good, but this is even better, and then, I wouldn't miss out on that if I ever left elten. Don't worry by the way, even though the website suggests German, the addon is in English.