The tweet below illustrates the specs of full screen vertical video on Twitter. Note how the 1080x1080 (1x1) part of the video is visible to users when the tweet appears in their timeline, we need the user to tap on the video to launch the full screen vertical video of 1080 (across) x 1920 (down) which fills the entire phone screen.

https://twitter.com/Gilbo/status/958674371643625474

Now check out this Amazon Prime Video UK tweet example of a full screen vertical video asset of 1080x1920 where the 1080x1080 section of the video is initially visible in timeline but when you tap it goes full screen.

https://twitter.com/GodsOnAmazon/status/861536555772645376

Few FYI's :-

i. You have to create these PTweets as standard old-school video PTweets NOT Website Cards (Video/Image) because we need the user tap to launch the full screen vertical video view (not take users through to the clients site like website cards do).

ii. No Desktop targeting, keep it iOS & Android only.

iii. As we need the user to tap the video to launch the full screen vertical video we shouldn't really use (or expect) full screen vertical video assets to drive clicks to clients site.

iv. We might want to think about placing a 'tap for full screen' prompt that is visible in the 1080x1080 so users know they can see the video full scReena.