Visualisation is out of sync

Spectrum and Level Elements post numerical values onto the Pipeline Bus as soon as they process the buffers, which is always way ahead of actual playback time. Synchronising the "playback" (i.e. the graphical display of the spectrum/level meter) with the actual audio is a problem already solved within GStreamer, and it's a genuinely difficult exercise to do it yourself (I already tried, and you have to deal with loads of different timestamps, discarding your own "buffers" etc.).

My proposed solution is to reimplement these Elements as Sinks that can be tee'd off from the main audio sink and synchronised appropriately.