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/
What is PeerTube? | JoinPeerTube

A free software to take back control of your videos! With more than 600,000 hosted videos, viewed more than 70 millions times and 150,000 users, PeerTube is the decentralized free software alternative to videos platforms developed by Framasoft

JoinPeerTube
@mojomoomoo and having to put up with tons of copyright problems
@arale_xan At the end of the days it's down to an individual to choose what works for them . Uploading a video directly on here the video can easily be downloaded and reshared by another user. Hosting sites do offer a level of protection to stop this but there is then the issue of usage by the host which is detailed in their terms.