The aoo, juce, and ff_meters sub-directories here are all managed subrepos from other github repos, using git-subrepo (https://github.com/ingydotnet/git-subrepo).
The aoo and JUCE ones are forks of mine in github, the ff_meters is the upstream author's repo.
This way all the code for the dependencies of sonobus is completely constained in this git repo, avoiding complexities of dealing with submodules, but having the benefit of being able to pull/push changes back from/to them at any time.
The Opus dependency is handled here with some pre-built static library versions of Opus for Mac, Windows and iOS, which can be found in the mac/windows/ios subdirectories here. For the linux build the opus library must be installed and available via pkg-config.