Does anyone know how to embed Youtube inline into Twitter Stream?

Amazingly Google is failing me on this question - wondering if anyone here knows how to do it. I have seen people with playable YouTube videos that display right in their stream like this:

https://twitter.com/pewdiepie/status/528640885664526338

That is a link to a specific tweet that utilizes this function, but if you check the main stream for that account @pewdiepie you can see the video appears playable in stream.

Thanks.

Twitter has always done this with my tweets automatically. Maybe you're not posting the full video URL when writing your tweet?

That's crazy - I have a bunch of accounts and I never get it - and about 90% of the YouTube videos I see posted on Twitter don't get it - it seems like only the major accounts with a massive amount of followers get that video inline - I am starting to think that is the cause.