Software falls under Process which is one of the four patentable subject matters for utility patents: Process, Machine, Manufacture and Composition of Matter. So software is patentable in the United States. However, software can also fall under the abstract idea exception and thus not be patentable.
Enfish LLC v Microsoft is the most important recent case. In its decision, the Supreme Court suggested that claims purporting to improve the functioning of the computer itself, or improving an existing technological process might not succumb to the abstract idea exception.
https://www.uspto.gov/web/offices/pac/mpep/s2106.html
Enfish LLC v Microsoft is the most important recent case. In its decision, the Supreme Court suggested that claims purporting to improve the functioning of the computer itself, or improving an existing technological process might not succumb to the abstract idea exception.
http://www.patentdocs.org/2016/05/enfish-llc-v-microsoft-cor...
That's your dividing line. My guess is that Fraunhofer's MP3 patents improve a technological process and are valid.