<!-- SOLUV · part 226 -->
onstructor is not saved, so copy the factory method directly.
		track.createInterpolant = this.createInterpolant;

		if ( hasTangents( this.settings ) ) {

			track.settings = {
				inTangents: this.settings.inTangents.slice(),
				outTangents: this.settings.outTangents.slice()
			};

		}

		return track;

	}

}

function scaleTangentTimes( tangents, timeScale ) {

	// tangents are [ time, value ] pairs, so only every second entry is a time

	for ( let i = 0, n = tangents.length; i !== n; i += 2 ) {

		tangents[ i ] *= timeScale;

	}

}

/**
 * The value type name.
 *
 * @type {string}
 * @default ''
 */
KeyframeTrack.prototype.ValueTypeName = '';

/**
 * The time buffer type of this keyframe track.
 *
 * @type {TypedArray|Array}
 * @default Float32Array.constructor
 */
KeyframeTrack.prototype.TimeBufferType = Float32Array;

/**
 * The value buffer type of this keyframe track.
 *
 * @type {TypedArray|Array}
 * @default Float32Array.constructor
 */
KeyframeTrack.prototype.ValueBufferType = Float32Array;

/**
 * The default interpolation type of this keyframe track.
 *
 * @type {(InterpolateLinear|InterpolateDiscrete|InterpolateSmooth|InterpolateBezier)}
 * @default InterpolateLinear
 */
KeyframeTrack.prototype.DefaultInterpolation = InterpolateLinear;

/**
 * A track for boolean keyframe values.
 *
 * @augments KeyframeTrack
 */
class BooleanKeyframeTrack extends KeyframeTrack {

	/**
	 * Constructs a new boolean keyframe track.
	 *
	 * This keyframe track type has no `interpolation` parameter because the
	 * interpolation is always discrete.
	 *
	 * @param {string} name - The keyframe track's name.
	 * @param {Array<number>} times - A list of keyframe times.
	 * @param {Array<boolean>} values - A list of keyframe values.
	 */
	constructor( name, times, values ) {

		super( name, times, values );

	}

}

/**
 * The value type name.
 *
 * @type {string}
 * @default 'bool'
 */
BooleanKeyframeTrack.prototype.ValueTypeName = 'bool';

/**
 * The value buffer type of this keyframe track.
 *
 * @type {TypedArray|Array}
 * @default Array.constructor
 */
BooleanKeyframeTrack.prototype.ValueBufferType = Array;

/**
 * The default interpolation type of this keyframe track.
 *
 * @type {(InterpolateLinear|InterpolateDiscrete|InterpolateSmooth)}
 * @default InterpolateDiscrete
 */
BooleanKeyframeTrack.prototype.DefaultInterpolation = InterpolateDiscrete;
BooleanKeyframeTrack.prototype.InterpolantFactoryMethodLinear = undefined;
BooleanKeyframeTrack.prototype.InterpolantFactoryMethodSmooth = undefined;

/**
 * A track for color keyframe values.
 *
 * @augments KeyframeTrack
 */
class ColorKeyframeTrack extends KeyframeTrack {

	/**
	 * Constructs a new color keyframe track.
	 *
	 * @param {string} name - The keyframe track's name.
	 * @param {Array<number>} times - A list of keyframe times.
	 * @param {Array<number>} values - A list of keyframe values.
	 * @param {(InterpolateLinear|InterpolateDiscrete|InterpolateSmooth)} [interpolation] - The interpolation type.
	 */
	constructor( name, times, values, interpolation ) {

		super( name, times, values, interpolation );

	}

}

/**
 * The value type name.
 *
 * @type {string}
 * @default 'color'
 */
ColorKeyframeTrack.prototype.ValueTypeName = 'color';

/**
 * A track for numeric keyframe values.
 *
 * @augments KeyframeTrack
 */
class NumberKeyframeTrack extends KeyframeTrack {

	/**
	 * Constructs a new number keyframe track.
	 *
	 * @param {string} name - The keyframe track's name.
	 * @param {Array<number>} times - A list of keyframe times.
	 * @param {Array<number>} values - A list of keyframe values.
	 * @param {(InterpolateLinear|InterpolateDiscrete|InterpolateSmooth)} [interpolation] - The interpolation type.
	 */
	constructor( name, times, values, interpolation ) {

		super( name, times, values, interpolation );

	}

}

/**
 * The value type name.
 *
 * @type {string}
 * @default 'number'
 */
NumberKeyframeTrack.prototype.ValueTypeName = 'number';

/**
 * Spherical linear unit quaternion interpolant.
 *
 * @augments Interpolant
 */
class QuaternionLinearInterpolant extends Interpolant {

	/**
	 * Constructs a new SLERP interpolant.
	 *
	 * @param {TypedArray} parameterPositions - The parameter positions hold the interpolation factors.
	 * @param {TypedArray} sampleValues - The sample values.
	 * @param {number} sampleSize - The sample size
	 * @param {TypedArray} [resultBuffer] - The result buffer.
	 */
	constructor( parameterPositions, sampleValues, sampleSize, resultBuffer ) {

		super( parameterPositions, sampleValues, sampleSize, resultBuffer );

	}

	interpolate_( i1, t0, t, t1 ) {

		const result = this.resultBuffer,
			values = this.sampleValues,
			stride = this.valueSize,

			alpha = ( t - t0 ) / ( t1 - t0 );

		let offset = i1 * stride;

		for ( let end = offset + stride; offset !== end; offset += 4 ) {

			Quaternion.slerpFlat( result, 0, values, offset - stride, values, offset, alpha );

		}

		return result;

	}

}

/**
 * A