Greasy Fork is available in English.
Add two download buttons to YouTube videos that allow you to download MP3 or Video without leaving the page with the option to choose the quality.
< Simple YouTube MP3/VIDEO Buttonsについてのフィードバック
Not to use with the old youtube, being that all are migrating to the new. It's in the script description.
For old youtube, I recommend this:
https://greasyfork.org/pt-BR/scripts/34613-download-mp3-video-for-youtube
Doesn't work on old Youtube
Title.