We have been waiting a long time to release this feature in the UE4 plugin, and our only possible implementation is to release a C++ interface for users to implement their own audio sampler.
Basically UE4 doesn't (yet ?) provide a way to extract audio waveform/spectrum that packages and works on every platform. The Visualization plugin only works in editor. We can't either rely on third party plugins.
The C++ interface is pretty easy, you can just setup the Spectrum or Waveform data from blueprint by inheriting a BP class from the C++ interface (PopcornFXAudioSamplerActor).
m_SpectrumData and m_WaveformData need to be setup either from BP or C++ then returned and.. that's it. The main thing is effects need to sample the "Master" channel. You need to make sure the spectrum or waveform data is power of two (256/512/1024 samples). 512 or 1024 samples is generally enough.
There are differences in units from PopcornFX and UE4's visualization plugin, you'll need to tweak that also..
We are waiting for UE4's new audio engine to release some kind of audio spectrum/waveform extract at runtime.
Let us know how it goes,