I have found that this forum's software only uses URLS that have "youtube.com" to create an instance of the video on the page. On the other hand, Youtube plays some games with URLs. They have also been using an alternate domain name, "youtu.be" (notice a different domain name as well as the absence of the .com extension). TCM just needs to add an extra line of code to create video instances with this "youtu.be" domain/extension also.
This has resulted in some not knowing how to post instances of videos into the forum.