Music licenses are the primary way you can protect yourself legally if you’d like to use a copyrighted song in some form of media. As a legal document, a license gives a person permission to use another artist’s copyrighted music for their own purpose for a fee.
Copyrighted music has the full protection of the United States government (you can learn more about that here).
Performing rights organizations (PROs) like ASCAP, BMI, and SESAC generally represent works for public performance royalties. Any sort of copyrighted music requires a music license to be used for anyone except for the writer that created the music. This includes playing copyrighted music in a public space, recording a copyrighted song, or using a copyrighted song alongside any sort of visual media — which specifically applies to sync licensing.