ytURL = https://www.youtube.com/watch?v=dQw4w9WgXcQ
do shell script "/usr/local/bin/youtube-dl -o ~/Desktop/DownloadedVideo.mp4 " + ytURL
(see photo for more info)
For the Run AppleScript action use the following example:
on run {input, parameters}
do shell script "/usr/local/bin/youtube-dl -o ~/Desktop/DownloadedVideo.mp4" & space & quoted form of item 1 of input
end run
Per CJK's comment, if you want to use a Run Shell Script action instead, then use:
Replace the default code with just:
/usr/local/bin/youtube-dl -o ~/Desktop/DownloadedVideo.mp4 "$1"