Music gets special treatment under copyright law, as the law applies differently to the piece of music itself (the composition) and each unique recorded performance of the piece of music (sound recordings). This means that there are two separate copyrights and very possibly two separate copyright holders for each music recording. Of course, all works in the public domain are free to use and reuse, but while the original compositions of classical composers such as Beethoven and Mozart may be in the public domain, recordings of recent performances of these works will not be.
This is further complicated by the fact that the US didn’t extend copyright protection to sound recordings until February 15, 1972, long after means for recording musical performances were widespread, leading to varying protections in each state. The Music Modernization Act (MMA) of 2018 created some quasi-copyright protections for these pre-1972 recordings depending on the date of their publication (not creation, an important distinction), resulting in a very complex landscape of copyright law applicable to music. For an in-depth overview of this landscape, check out Chapters 19 and 20 of the fourth edition of Kenneth Crews’s Copyright Law for Librarians and Educators (2020), available in Vogel Library.
Because music is such a creative medium of expression, fair use evaluations tend to lean against fair use. So there is a huge industry for the licensing of music. Thankfully, there are artists and recording studios that choose to make their recordings free to use as background for videos. Databases of these free-to-use songs, such as the Free Music Archive, are easily accessible online. For those songs and recordings not fitting into this category, there are several organizations that can help with securing permissions for use:
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