Just a few simple steps:
1. Visit the Google Webstore, download and enable the "tampermonkey" .
2. Click the link below to install the JS necessary for "tampermonkey".
3. After the installation is complete, it will automatically jump to the Google homepage. Open any youtube video and a red download button will appear, indicating that the extension is working properly.
4.Click the download button, it will jump to the download page, you can choose the format you want according to your needs.
Savefrom YouTube to local extension