>>Not sure the embedded html5 player (last I heard Flash was dead) within a browser has that option, but a standalone player like VLC should. It can raise the frequencies by the slowdown factor (it's mpeg compressed anyway, so it shouldn't be too hard to tell the sound encoder to multiply each tone's pitch by that number) so you hear the sounds lengthened but not deepened. So install a download helper and get the file from youtoobe (or yoochoob, ie. jućub as we call it here) and then watch it at your favorite speed.
>>
>>Someone did that and saved it at such - the opening credits song for a local soap opera we had here in late 80s, at factor ten. So it takes 20 minutes to hear a 2 minute song. Alcohol not required, gets you dizzy just trying to listen for the first few minutes.
>
>I don't understand something. How do you get the file (or a file) from youtube? I thought youtube videos can only be played in youtube. Am I wrong?

I use https://www.downloadhelper.net/