I use a custom URI combined with userjs(tempermonkey), mplayer and youtube-dl for same purpose. First you add custom URI in windows, lets call it magnet3 (this

I use a custom URI combined with userjs(tempermonkey), mplayer and youtube-dl for same purpose. First you add custom URI in windows, lets call it magnet3 (this should be a clue, it works just like torrent magnet links): [HKEY_CURRENT_USER\SOFTWARE\Classes\Magnet3] @="Magnet URI" "URL Protocol"="" "Content Type"="application/x-magnet" [HKEY_CURRENT_USER\SOFTWARE\Classes\Magnet3\shell] @="open" [HKEY_CURRENT_USER\SOFTWARE\Classes\Magnet3\shell\open] [HKEY_CURRENT_USER\SOFTWARE\Classes\Magnet3\shell\open\command] @="\"C:\\Users\\me\\Documents\\js\\youtube-dl mplayer.bat\" \"%1\"" then create your 'youtube-dl mplayer.bat' file (the %var:~9% nonsense removes first 9 characters from the passed link, '"magnet3:'): set var=%1 for /f "delims=" %%A in ('d:\_learning\youtube-dl.exe -f best -g "%var:~9%') do start "" "C:\Program Files\smplayer\smplayer" "%%A" or alternatively if your injected UserJS can extract direct link to media skip youtube-dl step: set var=%1 start "" "C:\Program Files\smplayer\smplayer" "%var:~9% now all you have to do is add userjs for the websites/services/players you want, for example I have a patched https://greasyfork.org/scripts/7096-convert-youtube-embeds-to-image-links/code/Convert%20Youtube%20Embeds%20to%20Image%20Links.user.js https://greasyfork.org/scripts/7096-convert-youtube-embeds-t... that replaces YT EMBEDs with a thumbnail linking to magnet3:link_to_yt, this is enough for starting mplayer on YT embeds. Rube Goldberg sequence of hacks, but works perfectly.