Old demos clean up after themselves

Each demo used to keep the frames its video was cut from, about half a gigabyte per demo, forever, so a busy machine filled up with demos. Obeya now deletes those frames a set time after a demo's last render, two weeks unless you choose otherwise under Keep frames in the Demos settings. Videos, pages and narration clips stay, so demos keep playing and re-render as before. The Demos settings also show how much space demos take and how much the last cleanup freed.