Music that is not in the public domain requires a license from the creator for use in YouTube videos. Music in the public domain typically includes any song or musical work that was published in 1922 or earlier.
Songs that are not in the public domain include all copyrighted works and royalty-free music. Licensed works may require a fee for the license and additional royalty fees. Royalty-free music may charge a license fee up front to use.
YouTube added a new feature in 2014 that tells content creators what is likely to happen if a video with copyrighted music is uploaded. The creators of the copyrighted music have the option to mute the sound on the video, completely block the video from being watched or decide to monetize the content.