Steps to reproduce:

• Go to YouTube and grab an embed link for a video, for example (www.youtube.com/embed/XvolhvLECPc).
• in a Confluence page, insert a widget connector macro, and paste the above URL.
• You will end up with a broken image and no player is shown:

Workaround:

Just grab the normal link from the YouTube link on the browser, which looks something like (http://www.youtube.com/watch?v=XvolhvLECPc).