Tinkerbell, here's how I do it.
I'll edit this if I need to and others can add how they do it in their own posts on here.
First of all, I don't even bother with the 'film roll' button. All you have to do is post a Youtube link and it will turn into the video. The thing to keep in mind is that it can't be just any Youtube link, it needs to be the 'share' kind. Here's how you do it.
1. Go to the Youtube site and find video that you want to post on here.
2. Still on the Youtube site, underneath that video and to the left of the number of views, you'll see a button marked Share. Click on that.
3. Copy the link that appears and paste it in a post here on this site.
That's it! Three easy steps. Give it a shot.