I already told you, creating a new thread for this won't get People to help you faster.
If you'd use the Forum search you'd know that other People can use Youtube on Whonix in a similar Setup just fine.
Here is an example: https://forums.whonix.org/t/tor-browser-cant-play-mp4-files/2052
YouTube is working using HTML5.
It works fine for a lot of other People, including myself, so there is no one who can help you since this isn't a known issue.
Yes, nobody can help, since you give no Information. I already asked you in post #7 whether you'd verified the Images and reinstalled VBox.
You ignored that.
Also, if you really want to figure out whether the issue lies with Whonix, try this: Set up a Debian VM on your System. Try Youtube on there. If it doesn't work, we know where the issue lies.
Have a nice day,