Video player card - when does the video play inline?


I have a player card that’s been validated and appears to work as intended. My question though is when exactly does a video play inline, particularly in mobile clients? I’ve noticed if I tweet a link to a card-enabled page, it’s rendered like this:

  1. Mobile - user must tap on tweet and enter a specific-tweet view in the app to watch the video
  2. Web - user must expand tweet to see the video player portion of the card

However, I also see tweets where videos play in the timeline without having to enter a specific tweet view or expand the tweet. This is what I would consider truly “inline.”

It seems like there are three levels for playing video:
A) Video plays truly “inline” in the timeline
B) Video plays in timeline, but tweet must be expanded (View media) / video plays in app but in separate view
C) User must follow link and video does not play on Twitter

Is it possible for all developers to get the A) experience? Or is this reserved for Twitter partners and possibly natively uploaded video? In the player card reference docs, the Vine post gets this treatment. I also see other A) videos in the timeline, but they appear to be Twitter Amplify partners.

Also, is it the case that B) type videos are automatically expanded if Twitter believes the tweet is especially relevant to a user?

The card reference doc states

specifying an MP4 file and indicating twitter:player:stream:content_type as “video/mp4” will allow playback of the video inline in our mobile applications.

And here, @rchoi provides some insight about how various Twitter clients render video

Our mobile clients know to use the twitter:player:stream. The web knows to use the twitter:player. Everything else has to link to the site to know how to render.

I assume these are in reference to B) type videos. Can you confirm?

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