class DownloadHelper {

  public List<TrackSelection> getTrackSelections(int periodIndex, int rendererIndex) {
    assertPreparedWithMedia();
    return immutableTrackSelectionsByPeriodAndRenderer[periodIndex][rendererIndex];
  }

  public  DownloadHelper(
      String downloadType,
      Uri uri,
      @Nullable String cacheKey,
      @Nullable MediaSource mediaSource,
      DefaultTrackSelector.Parameters trackSelectorParameters,
      RendererCapabilities[] rendererCapabilities);

}