I might just be bad at searching for shortcuts, but I couldn't seem to find a good youtube video/audio download shortcut that worked on all the videos I tried. Most of them seem to fetch the video id from the youtube link, download and parse the metadata file from google, then extract the download links. The problem for me was that these links didn't always fetch my video. Music video downloader.
So I made this shortcut to fix that. It uses qdownloader.net to do all of the complicated link parsing, then just scrapes the result page for links and finds the youtube ones. It lets you choose the quality of the video, or to download an mp3 of your video, and then you're free to save to the photo album, share with another app, or export to Dropbox. Feel free to edit if you use iCloud for storage or something (though you can always save to iCloud from the share menu). I set the name of the media to the name of the video so it's nice when you save. I also include the option to encode to.m4a audio after you download. Sometimes it's faster to download the low quality video and then extract the audio rather than wait for google to transcode an mp3.
Hope you guys find this useful:
Free music mp3s
From the YouTube app, use the share button -> more -> Shortcuts and select this shortcut. A menu will guide you with options. Similar method if you get the share menu open on any YouTube link from any app or web page. Just long press on the link and choose 'Share'.
Copy a YouTube video link to the clipboard, then run this Shortcut. It's best to go into the Shortcut first, then click the play button so that you can see the download progress bars. It still works if you just launch it directly, though expect some delays in between menu choices while the downloads magically happen in the background.
I used this recently to get some good music for a quick iMovie project on my phone.