What qualifies an og:video tag to be playable?

In the webmaster documentation, it states the following,

Use a secure URL for both the og:video:url and og:video:secure_url tags to make your video eligible to play in-line in News Feed. Note that your video is not guaranteed to play in-line based on a variety of factors.

Well the same tags work for other open graph share networks like iMessage, was wondering if someone could point me towards the relevant documentation on how to make videos playable.

Asked about a week ago