static getMediaQualityAtPosition_(position, contentTypeState) {
    // The qualityChangePositions must be ordered by position ascending
    // Find the last QualityChangePosition prior to the position
    const changePositions = contentTypeState.qualityChangePositions;
    for (let i = changePositions.length - 1; i >= 0; i--) {
      const qualityChange = changePositions[i];
      if (qualityChange.position <= position) {
        return qualityChange.mediaQuality;
      }
    }
    return null;
  }
Determines the media quality at a specific position in the source buffer.

@param {!number} position
 Position in seconds
@param {!shaka.media.QualityObserver.ContentTypeState} contentTypeState
@return {?shaka.extern.MediaQualityInfo}
@private