This is also a feature I would like to see, perhaps with additional restrictions (imo builder+, must go through approval queue regardless of user rank and take up 3-5 upload slots, same idea from a mod: forum #137909). forum #185863 implies that the current restriction on length/size comes from Twitter's length limit (2m 20s = 140s = Twitter video limit) and probably something to do the compression that they use, along with how large a (somewhat un)reasonably sized PNG can get.
There are a sizable amount of animations uploaded from other sites that require manual scraping. For example, animated ~source:https://www.bilibili.com/video ~source:https://www.youtube.com yields around 2k active posts. The inconvenience to find and scrape videos from these sites, particularly bilibili, suggests that a prospective uploader with a privileged account has sufficient reason to find, source, validate, tag, and upload such a video. This could be due to cultural relevance or artistic merit, two factors which already make Danbooru's existing collection invaluable for preserving and browsing art and culture throughout the history of the internet.
The sole goal of support for extended videos would be to archive fanworks (forum #127565), which often stretch past the 140s limit (if we're going to make a collaborative animation, might as well make it really good, tell a story, and span the full length of the background song, no?). Something like 10 mins/500 MB seems reasonable and covers all the relevant/on-topic/high quality animations. Stuff that's hand-animated frame by frame by a team of independent artists and high quality enough to the point that individual frames would merit posts of their own and would make it through modqueue if a blue user uploaded them. These are the works that I would like to see safe on this site and not at the mercy of the artist not wanting to have an internet presence anymore and nuking their socials. The criteria for approving long videos should be pretty strict: the individual frame criteria should definitely apply and overall quality and relevance (both to Danbooru and cultural) should be evident.
Concern over file size/spam seems overblown given that duration:>90 -making-of -source:https://twitter.com yields around 730 active posts. forum #123402 addresses potential malicious activity/spam and serverside ratelimiting should do a good job if needed (a sufficiently drunk builder should not be able to dump the entire bee movie in 8 minutes segments). Users scraping thousands of twitter posts with the bookmarklet is already well within the expected operations of the site. The rate at which somewhat long animations have been uploaded from any site that can host a video exceeding 140s over the duration that it's been allowed sits at well under 1/day. This is in contrast to Danbooru getting over 4k new posts on a typical day. I don't think an increased maximum video length would greatly affect the alter the load on the site infrastructure or alter Danbooru's focus or content composition.
