The "upload video" command don't explain it.
So, is there a limit? Size, lenght, etc?

I'm not sure. The instructions on the page say keep it to 1 minute or less, but a lot of videos go over that length by a lot. I think I've seen a couple at 5 minutes.

I've yet to find a length or size limit. How long/big is the video you're wanting to upload.

quick. upload an entire movie and see if it fully loads.

I still need to check, but I want to upload a game progress video the next month and I want to know the limits so I can edit it or split it in parts.

Well, the longest video I've uploaded is 8 minutes 18 seconds, and the largest video I've uploaded is 67.6 MB. Don't know if that helps.

I saw some videos with over 25 mins on rule34.xxx (with around ~140mb in size), but their resolution were quite bad as you might guess. Size is probably the main limitation.

I recently uploaded a video that was 96.3 MB at 720p. I was not able to upload the 1080p version at 164.6 MB, so if it's a size limit, that gives us a range it could be in. The video was 1 minute and 10 seconds.