WATCHES the cut. Composites every video layer at each requested frame and returns ONE contact sheet — the frames as labelled cells of a single grid image — plus, per cell, the visibleClipIds that contributed pixels and a fingerprint. Pass frames (timeline frame numbers, max 12). Use after every edit: this is the only tool that shows what actually PLAYS, as opposed to what get_timeline says is arranged. SAMPLE THE CUT POINTS AND THE MIDDLE OF EACH SECTION, not only frame 0. An entrance animation that never resolves, a graphic clipped by its own box, an offline clip rendering black — all look perfect in get_timeline and are obvious here. USE pixels:false FOR A CHEAP SWEEP. visibleClipIds plus nonBlankRatio confirms 'the right clip is in every slot and none of them is black' across a dozen positions with no image cost; spend pixels on the few frames where you must judge typography, framing or timing.