function addGroupId(level, type, id) {
  switch (type) {
    case 'audio':
      if (!level.audioGroupIds) {
        level.audioGroupIds = [];
      }

      level.audioGroupIds.push(id);
      break;

    case 'text':
      if (!level.textGroupIds) {
        level.textGroupIds = [];
      }

      level.textGroupIds.push(id);
      break;
  }
}
@module LevelHelper
Providing methods dealing with playlist sliding and drift