Create a positives sample grope (classifier model) by adding stuff from adult websites into your site, then when a new upload matches the Adult content positive video recognition don’t link the video. (If you don’t want any adult content don’t link videos used in the classifier, either.) The only bottle neck is for copyrighted content, copyright holders usually don’t publish a classifier for their content.
There are some Copy Protection systems that try to add an id, usually called a “fingerprint”, to the optional text block in an mp4. This id is then used to determiner the origin of the mp4. You could block mp4s using this id system, but that wouldn’t control for DVD-rips and other valid copyrights that don’t have an id system.