The best open source alternative to FMOD Ex is OpenAL Soft. If that doesn't suit you, our users have ranked six alternatives to FMOD Ex and five of them is open source so hopefully you can find a suitable replacement. Other interesting open source alternatives to FMOD Ex are PortAudio, RtAudio, AudioKit and SoLoud.
OpenAL Soft is an LGPL-licensed, cross-platform, software implementation of the OpenAL 3D audio API. It's forked from the open-sourced Windows version available originally from openal.org's SVN repository (now defunct).
PortAudio is a cross platform, open-source, audio I/O library. It provides a very simple API for recording and/or playing sound using a simple callback function.
RtAudio is a set of C++ classes that provide a common API for realtime audio input/output across Linux, Macintosh OS-X and Windows operating systems. RtAudio significantly simplifies the process of interacting with computer audio hardware.
AudioKit is the leading open-source audio framework. It powers millions of app installs. AudioKit allows developers to quickly add professional audio functionality to iOS, macOS, and Apple Watch apps.
SoLoud is portable - the c/c++ code base is written in portable way, and the code has been used on various platforms including windows, osx, linux, as well as android and even ps4. (I'm not responsible for many of the platforms, though, and for licensing reasons, ps4 code is...
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