message: state time can't be less than 0
diff: import { Seconds } from "../type/Units";
  import { Timeline, TimelineEvent } from "./Timeline";
  +import { assertRange } from "./Debug";
  export type BasicPlaybackState = "started" | "stopped";
  export type PlaybackState = BasicPlaybackState | "paused";
  @@ -48,6 +49,7 @@ export class StateTimeline<AdditionalOptions extends {} = {}> extends Timeline<S
  * @param options Any additional options that are needed in the timeline.
  */
  setStateAtTime(state: PlaybackState, time: Seconds, options?: AdditionalOptions): this {
  + assertRange(time, 0);
  this.add(Object.assign({}, options, {
  state,
  time,
  