Okay, so for an example:
First, try and play Drake – Hell Yeah as an embedded YouTube video. If you do so via clicking on the hyperlink in SO — it will work. But, if you copy/paste the URL into a new tab — it will not.
You will see an error message: “This video contains content from UMG. It is restricted from playback on certain sites. Watch on YouTube.”
Now, take that same link ( http://www.youtube.com/embed/muUEyXj-iqk ) and paste it as a post on a Facebook wall. The song happily plays.
What sort of communication is going on to allow Facebook to play an embedded video, but playing the same video from YouTube itself does not work?!
Not sure where I should start looking for this magic. Is it communicated through headers…? Or some other clever coding…? Or an agreement between YouTube and Facebook?
UPDATE: So, if you click the URL that I have hyperlinked to — it will play. But, if you copy/paste the URL into your browser – it will not play. I assume that YouTube is looking at the referring link for the URL and determining if the video is playable based on where the hit came from. Since it is coming from a website when clicked, but not from anyone specifically when copy/pasted, I get different results?
Embed restrictions are set by the content owner. In this case Vevo could have created a whitelist of places their video can be viewed. Because you can see it on http://www.facebook.com it means it could be included in this whitelist. Some of the details about these policies are here on the YouTube content id faq.
http://www.youtube.com/t/contentid_more
The closest answer to this issue is the one related to being blocked in an uploader’s region. The help page should be updated to also include site restrictions.