No, but you can link to an external video. Unfortunately videos are very taxing on servers (and therefore expensive to deal with), so it's unlikely we'll see them in Lemmy in the near future.

It's up to the client on how to render them. Most videos I encounter in Lemmy are linked from outside sources or are on YouTube.

• Lemmy-UI has no or limited support for anything but images.
• Tesseract is on the other end of the spectrum and supports pretty much every kind of media.
• Photon supports GIFs and native (mp4, webm) videos.
• Other UIs and mobile apps, I haven't kept as up-to-date on but are typically somewhere between Lemmy-UI and Photon's level of media support.

Edit: In addition to what clients support, it's also up to each instance admin to define what media they allow to be uploaded. Among the possible configuration options are:

• Whether to allow any media uploads at all
• The max size of the media they'll allow users to upload
• Whether to allow videos or just static images
• Whether to convert videos to GIFs or static images
• Whether the media subsystem (pict-rs) can process the upload before the upload request times out. I think that's 10 seconds which limits direct uploads to short videos.

Like others have said, hosting videos is expensive both in areas of storage and bandwidth. Most Lemmy instances are run by volunteers at their cost or operate solely on donations. Admins typically ask users to host those off-server (Imgur, YouTube, Catbox, etc) and restrict what can be uploaded directly to reasonable limits.

I posted a .gif in a comment the other day just using the base lemmy.world interface on desktop and it Just Worked. I don't know about other clients/UI's.

Why is it not good enough to submit a link? I only come to sites like this for the comments, anyway.

I really hope not.

Luckily hosting videos require quite a lot of resources so it will be too much for many smaller, selfhosted instances, which will hopefully contain the spread of it.