What determines if a twitter card gets rendered in your timeline?


#1

When I tweet youtube links like https://www.youtube.com/watch?v=tfollv1111I , the twitter card renders in the timeline and the video is playable from within the timeline.

However other links with valid twitter cards like http://imgur.com/0BWTan0 do not render in the timeline, only in the detail view for the tweet.

What determines if a twitter card gets rendered in your timeline?