YT-Download

This extension works together with i local installation of "ffmpeg" and "YouTube-DL" (from github).
https://github.com/ytdl-org/youtube-dl
https://github.com/FFmpeg/FFmpeg

My extension passes information to YouTube-DL, that does the actual download.
Here is a list of supported sites (from youtube-dl)
https://github.com/ytdl-org/youtube-dl/blob/master/docs/supportedsites.md

Install instructions:
1: Install the Opera Extension
2: Install the "MS Visual C++ 2010 SP1 Redist (x86)" (Link will display in the Opera Extension)
3: Install the "YT-Download local installation" (Link will display in the Opera Extension)

Have fun!