Kdenlive: Preview Rendering -- Odds and Ends

The Kdenlive developer Jean-Baptiste Mardelle is incredibly busy these days adding cool new features to the current development branch. So we now get preview rendering for smooth playback of our timelines, even with CPU-bogging effects applied. This really good stuff will show up later this year in the next 16.08 stable Kdenlive release. So what is this preview rendering?