https://chrome.google.com/webstore/detail/open-in-mpv/epaldpobheocfkfioepkcalnlhlgpcag/

I modified the IINA Chrome extension to work with MPV so I'm not required to have a background process running like what the alternatives need.

The only caveat is that you need to assign MPV to the ytdl:// url scheme.

On a Mac this can be achieved by using https://github.com/Lord-Kamina/SwiftDefaultApps