If channel A uploads a video copied from channel B, then makes a copyright claim against channel B, how does an automated system determine which owns the rights

If channel A uploads a video copied from channel B, then makes a copyright claim against channel B, how does an automated system determine which owns the rights? Certainly it would seem in most cases that we should presume channel B has the copyright, since they uploaded first. But there is a very economically important class of videos where infringers will tend to be the first to upload (movies, TV shows, etc.). I don't really see how an automated system solves this problem without making any mistakes. Especially because the law (DMCA) puts the onus on the service provider to take down or face liability.