Well, not really.
“Other platforms” might allow you to upload a video file and then they might throw that into a video element, and that’s great and all. But that’s kinda naive. If you uploaded a 4K 60fps video, that might be just fine for you, but if one of your contacts comes along and wants to check out your post on a mobile phone with a regular mobile network connection, they’ll have a hard time.
The only “fediverse” implementation that is doing actual transcoding is PeerTube - and PeerTube is a project that does nothing but video sharing. They can literally spend all their development effort on making video work, and that’s good for them. But as I said, video hosting is absolutely nothing diaspora* is focussing on, and given the amount of work required, its unrealistic to expect diaspora* to do that. Embedding PeerTube might be a thing in the future, though.
(I’m ignoring some transcoding abilities in platforms that transcode gifs into mp4s etc, that’s not really relevant here.)