func: static int calculate_bitrate(AVFormatContext *s)
  
  {
  
      AVIContext *avi = s->priv_data;
  
      int i, j;
  
      int64_t lensum = 0;
  
      int64_t maxpos = 0;
  
  
  
      for (i = 0; i<s->nb_streams; i++) {
  
          int64_t len = 0;
  
          AVStream *st = s->streams[i];
  
  
  
          if (!st->nb_index_entries)
  
              continue;
  
  
  
          for (j = 0; j < st->nb_index_entries; j++)
  
              len += st->index_entries[j].size;
  
          maxpos = FFMAX(maxpos, st->index_entries[j-1].pos);
  
          lensum += len;
  
      }
  
      if (maxpos < avi->io_fsize*9/10) // index does not cover the whole file
  
          return 0;
  
      if (lensum*9/10 > maxpos || lensum < maxpos*9/10) // frame sum and filesize mismatch
  
          return 0;
  
  
  
      for (i = 0; i<s->nb_streams; i++) {
  
          int64_t len = 0;
  
          AVStream *st = s->streams[i];
  
          int64_t duration;
  
  
  
          for (j = 0; j < st->nb_index_entries; j++)
  
              len += st->index_entries[j].size;
  
  
  
          if (st->nb_index_entries < 2 || st->codec->bit_rate > 0)
  
              continue;
  
          duration = st->index_entries[j-1].timestamp - st->index_entries[0].timestamp;
  
          st->codec->bit_rate = av_rescale(8*len, st->time_base.den, duration * st->time_base.num);
  
      }
  
      return 1;
  
  }
  