warp( startTimeScale, endTimeScale, duration ) {

		const mixer = this._mixer,
			now = mixer.time,
			timeScale = this.timeScale;

		let interpolant = this._timeScaleInterpolant;

		if ( interpolant === null ) {

			interpolant = mixer._lendControlInterpolant();
			this._timeScaleInterpolant = interpolant;

		}

		const times = interpolant.parameterPositions,
			values = interpolant.sampleValues;

		times[ 0 ] = now;
		times[ 1 ] = now + duration;

		values[ 0 ] = startTimeScale / timeScale;
		values[ 1 ] = endTimeScale / timeScale;

		return this;

	}
Changes the playback speed, within the passed time interval, by modifying
{@link AnimationAction#timeScale} gradually from `startTimeScale` to
`endTimeScale`.

@param {number} startTimeScale - The start time scale.
@param {number} endTimeScale - The end time scale.
@param {number} duration - The duration.
@return {AnimationAction} A reference to this animation action.