You can't re-post the content as your own. However, the video exists as public on YouTube today. You can simply embed the YouTube player right on your forum post or simply link them to the YouTube video. PHPBBs in general will support embedding of a YouTube player into a forum post. Them watching it in the public space where it is currently provided is perfectly fine.
"In anything, if you want to go from just a beginner to a pro, you need a montage." /w TankSpot WTB Montage for Raiders.