docs: protected ParsableBox createMvhd(Movie movie) {
          MovieHeaderBox mvhd = new MovieHeaderBox();
          mvhd.setVersion(1);
          mvhd.setCreationTime(getDate());
          mvhd.setModificationTime(getDate());
          mvhd.setDuration(0);//no duration in moov for fragmented movies
          long movieTimeScale = movie.getTimescale();
          mvhd.setTimescale(movieTimeScale);
          // find the next available trackId
          long nextTrackId = 0;
          for (Track track : movie.getTracks()) {
              nextTrackId = nextTrackId < track.getTrackMetaData().getTrackId() ? track.getTrackMetaData().getTrackId() : nextTrackId;
          }
          mvhd.setNextTrackId(++nextTrackId);
          return mvhd;
      }