project clearly links to open source projects
- ALSA is released under the GPL (GNU General Public license) and the LGPL (GNU Lesser General Public License).
- JACK is under the terms of the GNU GPL and LGPL licenses.
- adishavit/argh is released under BSD 3-clause "New" or "Revised" License.
- fmtlib is relased under BSD 2-clause "Simplified" License.
- spdlog is released under the MIT Licence.
- linking against the stdlib is exempted from having to be GPL.
- system calls like inotify are considered normal use: http://inotify.aiken.cz/?section=inotify&page=faq
- Qt is released under GPL & LGPLv3 licenses.
- xlib looks like bsd 3-clause or similar.
That being the case, looks like LGPL is the most restrictive required licence.
And since this is an end user program which I dont imagine anyone would ever link to I'll go with the GPLv2 for my parts.