the overlay button (second button from the left on the toolbar) toggles overlay mode on and off. when overlay is enabled, the video you see is updated constantly.the difference from preview is that the osprey driver uses the fastest and most efficient drawing method it can. normally, with direct draw enabled and working, it draws at the full frame rate (30 per second) with minimal processor overhead.

    note that the preview and overlay buttons behave like radio buttons that cancel each other - you do not have to shut off preview in order to start overlay.