When you're on the video page, click on the top little bar thing were it has the link. Once everything is highlighted, go to Edit and click Copy. Then go make the message you want to write and go back up to Edit and click Paste. Or, instead of going to Edit, you could use shortcuts:
Copy: Ctrl C
Paste: Ctrl V
It's the same for most computers. It may not work for yours though.
Copy: Ctrl C
Paste: Ctrl V
It's the same for most computers. It may not work for yours though.