func: static AVRational update_sar(int old_w, int old_h, AVRational sar, int new_w, int new_h)
  
  {
  
      // attempt to keep aspect during typical resolution switches
  
      if (!sar.num)
  
          sar = (AVRational){1, 1};
  
  
  
      sar = av_mul_q(sar, (AVRational){new_h * old_w, new_w * old_h});
  
      return sar;
  
  }
  