func: static void compute_frame_duration(int *pnum, int *pden,
  
                                     AVFormatContext *s, AVStream *st, 
  
                                     AVCodecParserContext *pc, AVPacket *pkt)
  
  {
  
      int frame_size;
  
  
  
      *pnum = 0;
  
      *pden = 0;
  
      switch(st->codec.codec_type) {
  
      case CODEC_TYPE_VIDEO:
  
          *pnum = st->codec.frame_rate_base;
  
          *pden = st->codec.frame_rate;
  
          if (pc && pc->repeat_pict) {
  
              *pden *= 2;
  
              *pnum = (*pnum) * (2 + pc->repeat_pict);
  
          }
  
          break;
  
      case CODEC_TYPE_AUDIO:
  
          frame_size = get_audio_frame_size(&st->codec, pkt->size);
  
          if (frame_size < 0)
  
              break;
  
          *pnum = frame_size;
  
          *pden = st->codec.sample_rate;
  
          break;
  
      default:
  
          break;
  
      }
  
  }
  