title: FFmpeg does not see setted frontend0 parameters
body: <p>I am setted DVB parameters like this :</p>
  
  <pre><code>static struct dtv_property props[] = {
  { .cmd = DTV_DELIVERY_SYSTEM, .u.data = SYS_DVBT2 },
  { .cmd = DTV_FREQUENCY,       .u.data = 474000000 },
  { .cmd = DTV_MODULATION,      .u.data = QAM_64 },
  { .cmd = DTV_INVERSION,       .u.data = INVERSION_AUTO },
  { .cmd = DTV_INNER_FEC,       .u.data = FEC_AUTO },
  { .cmd = DTV_TUNE ,           .u.data = FE_SET_FRONTEND},
  { .cmd = DTV_BANDWIDTH_HZ ,   .u.data = 8 },
  };
  
  static struct dtv_properties dtv_prop = {
  .num = 7, .props = props
  };
  </code></pre>
  
  <p>So then I am trying to use this setted DVB use in FFmpeg but it gets error.Why FFmpeg doesn't see Frontend0?</p>
  
  <pre><code>if(avformat_open_input(&amp;pFormatCtx, "/dev/dvb/adapter0/frontend0", NULL, NULL)!=0)
  {
      printf("error");
      return -1;
  }
  </code></pre>