Do you have the Pin It button on your screen?
I just went to Youtube, started a quilt pattern video, paused it, hit the Pin It button, and Pinterest offered me my choice of all the quilt pattern videos in my "Quilt Pattern" folder. I went to Pinterest and, sure enough, I can play the tutorial from there. (Thanks! I didn't know this was possible!) I just tried it again, and it seems to work even if I haven't added a video to my personal folder.
I have Chrome, which seems to periodically remove my Pin It button from the toolbar. I just Google "Add Pin It Button" to get the instructions again.