Technically, you can't. Nostr is only for text-based json notes, not media files of any kind. When you "upload" a video through a Nostr client, you are really just uploading to a media hosting service. Typically you can find out which one by looking at your settings. Then the URL that points to that media file at the host's domain address will be added into your text note, but Nostr relays will only have that text note with the URL saved to them, not the media file.

Some media hosts will allow larger files, but most will cap out at 100MB or less for those who don't have a paid account. To upload larger files than that, you will either need to pay for hosting with a provider like nostr.build or satellite.earth, or you will need to host it yourself, which can be done using your own Blossom server.