All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
The basic principle is that it is permissible to post videos as long as their content is permissible, and it is not obligatory to investigate and verify the legality of their content.
However, if a person knows or believes that a video most likely uses pirated content and constitutes copyright infringement, it is impermissible to broadcast it because it is impermissible to infringe the copyrights and other intellectual property rights, according to the Fataawa issued by the Fiqh councils and the general majority of contemporary scholars. Broadcasting pirated videos involves cooperation in committing this sin and an approval of it.
For more benefit on violating copyrights, please refer to Fataawa 361939, 384226, 306484, and 83969.
Allah Knows best.