What License Governs the Libopus Library?

This article provides a clear overview of the specific open-source license that strictly governs the distribution and modification of the libopus library. It details the core terms of this license, explains the accompanying patent grant, and outlines what these terms mean for developers integrating the library into their software.

The 3-Clause BSD License

The libopus library, which is the reference implementation of the IETF Opus audio codec, is distributed under the 3-Clause BSD License (also known as the “Modified BSD License” or “New BSD License”).

This is a highly permissive open-source license that allows developers to freely use, modify, and distribute the software in both source and binary forms.

Core Requirements of the License

To comply with the 3-Clause BSD License when distributing libopus (modified or unmodified), you must adhere to three straightforward conditions:

  1. Retain Copyright Notices in Source Code: If you redistribute the source code of libopus, you must retain the original copyright notice, the list of conditions, and the disclaimer.
  2. Include Copyright Notices in Binary Form: If you redistribute libopus in binary form (such as compiled libraries or pre-packaged applications), you must reproduce the original copyright notice, the list of conditions, and the disclaimer in the documentation or other materials provided with the distribution.
  3. Restrictions on Endorsements: You cannot use the names of the copyright holders (such as the Xiph.Org Foundation, Skype/Microsoft, or Broadcom) or the names of their contributors to endorse or promote products derived from the software without prior written permission.

The Software Disclaimer

The license includes a standard “AS IS” disclaimer. This means the contributors of the libopus library provide no warranties of any kind, and they cannot be held liable for any damages arising from the use of the software.

The Accompanying Patent License

While the copyright of the code is covered by the 3-Clause BSD License, the Opus codec itself is backed by strong patent grants.

Because the Opus codec was standardized by the Internet Engineering Task Force (IETF), the primary developers (including Xiph.Org, Microsoft, Broadcom, and Octasic) have granted a royalty-free, perpetual patent license to anyone using, making, selling, or importing implementations of the codec, including libopus.

Note: This patent grant includes a reciprocity clause. If you launch patent litigation claiming that the Opus codec infringes on your patents, your royalty-free patent license for Opus is immediately terminated.

Summary of Usability

Because of the combination of the permissive 3-Clause BSD License and the royalty-free patent grant, libopus can be integrated into both open-source projects (such as GPL-licensed software) and proprietary, commercial, closed-source applications without any licensing fees or royalty payments.