Lin uploads her cover of John’s song to YouTube, but then Content ID claims it and the video is blocked. What should Lin have done before uploading the video?

Lin needed to obtain a mechanical license from John (or his publisher) before uploading her cover song. This license grants permission to reproduce and distribute a copyrighted musical composition. Without it, John's Content ID system correctly identified the unauthorized use of his intellectual property, leading to the video's blocking. Giving credit in the description is good practice but does not grant legal permission for use. Altering the song to evade Content ID is a circumvention tactic and doesn't resolve the underlying copyright infringement. Content ID does not automatically block all cover songs; it blocks those for which rights holders have not granted permission or set specific policies.