If you are new to #mastodon, migrating from #twitter and you love to post videos, please consider posting your video over at a hosting site such as Youtube or Vimeo (others exist). Then post the link, it should show and play in your Toot.
It saves your server from having to store and stream huge quantities of extra data.
I'm going to add into here that federated hosting exists in the form of #peertube as well which is worth a look at. https://joinpeertube.org/
C'est quoi PeerTube ? | JoinPeerTube

Un logiciel libre pour reprendre le contrôle de vos vidéos ! Avec plus de 600 000 vidéos hébergées, visionnées plus de 70 millions de fois et 150 000 utilisateur⋅ices, PeerTube est l'alternative libre et décentralisée aux plateformes vidéos proposée par Framasoft

JoinPeerTube

@mojomoomoo anyone have issues getting Vimeo to play inline? Let me know if you can see this:

https://vimeo.com/770244775

Flip thru: La Jeté

Vimeo
@colorblindcowboy @mojomoomoo I see it as a link, not as an embedded video. Mind you, I'm looking from my Android phone in the Mastodon app. Let me check from my computer
@Grand_Focus @mojomoomoo thanks for checking. I can see it as a video via the mobile browser, but I know the apps all treat media differently.
@colorblindcowboy @mojomoomoo From my laptop, in Chrome, I see the embedded video, with the link directly above it.