docs: protected ParsableBox createMoof(long startSample, long endSample, Track track, int sequenceNumber) {
          MovieFragmentBox moof = new MovieFragmentBox();
          createMfhd(startSample, endSample, track, sequenceNumber, moof);
          createTraf(startSample, endSample, track, sequenceNumber, moof);
  
          TrackRunBox firstTrun = moof.getTrackRunBoxes().get(0);
          firstTrun.setDataOffset(1); // dummy to make size correct
          firstTrun.setDataOffset((int) (8 + moof.getSize())); // mdat header + moof size
  
          return moof;
      }