On YouTube, it is common for users to upload videos that they have created or own the rights to. However, some users may attempt to avoid copyright infringement by uploading mirrored versions of videos that they do not own the rights to. In these cases, does the original YouTuber still have any copyrights over a mirrored version of their video? Can they still make a claim against the uploader for using their content without permission?
First of all, taking a video made by someone else, making alterations and then distributing the resulting work is probably already a copyright violation. There are exemptions like fair use (check the comments for an example), but just taking a whole video, mirroring it and reposting it without any own contribution very likely does not constitute fair use. The people who do that don't avoid copyright infingement. They just try to avoid getting caught by any automatic system YouTube has in place to detect copyright infringements. But avoiding automatic filters does not mean to avoid DMCA takedown notices, cease&desist letters or lawsuits from real humans who find a mirrored version of their video and feel that their copyright was violated.
However, alterations to a creative work can be a creative work in itself. So regardless of the fact that one violated copyright in creating a derivative work, that derivative work might still be eligible for copyright in its own right. That means someone who reposts a video originally made by party A and then altered by party B would violate the copyright of both A and B at once and thus expose themselves to potential legal actions from either party.
But the question is if simply mirroring a video constitutes the necessary threshold of originality to make the resulting work eligible for copyright. In most courts, it probably would not.