This has two components: 1. using the visibility API (or some other mechanism), detect that a Shumway instance isn't visible; either because it's in a non-active tab or because it's outside the viewport. For these instances, stop the main event loop and don't call rAF. 2. Under the same circumstances as above, but perhaps after a certain delay, tear down the output canvas. We can re-create that when the SWF becomes visible again.