YouTube.com has started automatically using the shorter “.be” format for video URL links. In some cases this disrupts the auto preview capability of Facebook when sharing or posting a YouTube video.
Short YouTube video link: http://youtu.be/uLMmCepJyFY
Long YouTube video link: http://www.youtube.com/watch?v=uLMmCepJyFY
In order solve this first get the long YouTube video URL:
1. Select the “Share” option below the video player.
2. Select the “Show options” to the right of the link.
3. Select the “Long Link” check box.
This will change the video link to the long format and in most cases solve the problem when pasted into the Facebook share box.
If the problem persists then the share preview can be forced by adding the the following text suffix to the end on the long link, without the quotes:”&feature=share”.