The key here is manual moderation. At NodeBB we also have had our fair share of spam companies trying to build scripts to post things, and the only foolproof solution is manual moderation via a post queue for new users.
The downside, of course, is that they takes effort to maintain, and is a barrier to entry for new accounts.
Edit: Why does shadow banning feel like such an elegant solution? Everything has tradeoffs and I feel like shadow banning has tons of upside and very little downside. What am I missing?
There are cases in which explicit and obvious moderation results in retaliation, including DDoS and hacking attacks.
Various soft fail mechanisms, including shadowbanning, degraded performance, errors, authentication failures, etc., may help avoid this.
The question is what adversarial model you're facing: is it some random pr0n / SEO / affiliate / fraudster, or is it a "nice website you gots heyah, be a shame if anyting happen' to it" squad?
The only risk I can think of is that someone will upload the video and then livestream its playback on your platform with your branding using a separate livestreaming tool.
I.e. shadow banning semantically cannot work with a site that is geared toward publishing content, because the content is supposed to be visible to visitors who are not authenticated. If it isn't visible, that is painfully obvious.
Shadow banning only works when only authenticated users can see any content at all; then we arrange for only the offender to see content they have created. This works as long as the offender doesn't create multiple accounts.
(You need something slightly more clever, like allowing the content to be viewed from the same IP address as the last known address for that offender, plus some surrounding range (e.g. IPv4 class C subnet)).
It’s kind of easy to check if your posts are visible for not logged in users so you aren’t fooling bots and spammers, just real people. And the bots don’t care about moderation drama but the real people do, no matter if the moderation is proper or not. It always looks really unfair.
This invites a couple of questions. One, do the spammers care that the content is actually visible? Two, does spam come from more accounts or the same accounts?
Unrelated, but seeing NodeBB reminded me of the old days when installing forums for communities. phpBB2, vBulletin, downloading plugins and themes, etc. Oh, the nostalgy for the old web is amazing...
The downside, of course, is that they takes effort to maintain, and is a barrier to entry for new accounts.