libopus is currently supported on Windows, Mac, and Linux in UE4. I haven’t tried making it for Android, but these steps may work.
There is an android.mk for libopus here:
https://android.googlesource.com/platform/external/libopus/+/master
Compile a libopus.a and libspeex_resampler.a for ARM and optionally x86.
Create an opus-1.1/Android/ARMv7 directory and optional opus-1.1/Android/x86 directory and copy the .a files into them.
Making the following addition to libOpus.build.cs in Engine/Source/ThirdParty/libOpus:
else if (Target.Platform == UnrealTargetPlatform.Android)
{
PublicAdditionalLibraries.Add(LibraryPath + "/Android/ARMv7/libopus.a");
PublicAdditionalLibraries.Add(LibraryPath + "/Android/ARMv7/libspeex_resampler.a");
PublicAdditionalLibraries.Add(LibraryPath + "/Android/x86/libopus.a");
PublicAdditionalLibraries.Add(LibraryPath + "/Android/x86/libspeex_resampler.a");
}