Move 1 to 200 timeline clips by the same delta_ms (negative moves earlier), keeping their spacing and their tracks. All or nothing: an unknown clip id, a clip on a locked track, a clip pushed before 0 or past the timeline cap, or a landing that overlaps a clip you did not list refuses the whole call, names the first offending clip, and moves nothing; an overlap refusal gives the nearest delta_ms that fits. Scenes on the main track keep their order and are not clips; use reorder_scenes for them.