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• Why use sysconf(_SC_NPROCESSORS_CONF) to get the number of CPU cores in x264 ?

  5 novembre 2017, par bknieven

  I find x264 use sysconf(_SC_NPROCESSORS_CONF) instead of sysconf(SC_NPROCESSORS_ONLN) to get the number of CPU cores.

  Here is the code snippet in x264/common/cpu.c :

  ...
  
  #ifdef __ANDROID__
  
      // Android NDK does not expose sched_getaffinity
  
      return sysconf( _SC_NPROCESSORS_CONF );
  
  #else
  
      ...
  
  ....

  And I find the difference between _SC_NPROCESSORS_CONF and _SC_NPROCESSORS_ONLN in this manual :

  sysconf (_SC_NPROCESSORS_CONF) which returns the number of processors
  the operating system configured. But it might be possible for the
  operating system to disable individual processors and so the call
  sysconf (_SC_NPROCESSORS_ONLN) returns the number of processors which
  are currently online (i.e., available).

  I have two questions :

  1. What is the difference between "the number of processors the operating system configured" and "the number of processors which are currently online" ?
  2. Why x264 use _SC_NPROCESSORS_CONF in Android to get the number of CPU cores ?

• Anomalie #4257 : Impossible de lire certaines descriptions XML et validation XML bloquée par écran...

  28 décembre 2018

  Au temps pour moi, c’est dans le core et non dans SVP :
  https://core.spip.net/projects/spip/repository/entry/branches/spip-3.2/ecrire/plugins/infos_paquet.php#L81

  <span class="CodeRay"><span class="local-variable">$h</span> = <span class="predefined">$GLOBALS</span>[<span class="string"><span class="delimiter">'</span><span class="content">meta</span><span class="delimiter">'</span></span>][<span class="string"><span class="delimiter">'</span><span class="content">adresse_site</span><span class="delimiter">'</span></span>] . <span class="string"><span class="delimiter">'</span><span class="content">/</span><span class="delimiter">'</span></span>
          . <span class="predefined">substr</span>(<span class="string"><span class="delimiter">"</span><span class="local-variable">$dir_plugins</span><span class="local-variable">$plug</span><span class="content">/</span><span class="delimiter">"</span></span>, <span class="predefined">strlen</span>(_DIR_RACINE)) . <span class="string"><span class="delimiter">'</span><span class="content">paquet.xml</span><span class="delimiter">'</span></span>;
  </span>
  Télécharger

  En remplaçant $GLOBALS[’meta’][’adresse_site’] . ’/’ par ’../’

  Ça passe. Mais je suppose qu’il y a une syntaxe plus générale pour calculer le chemin relatif à ecrire/

• FFProbe generated data don't seem to agree with calculated data using ffmpeg libraries

  18 janvier 2020, par ark1974

  Using ffmpeg library avformat I am trying to check if the ffprobe generated data agrees with the data generated by the library. The code objective is to try to seek to the nearest key frame. When trying to seek at 100 frame or less, the codes returns 0 all the time.
  When trying to seek at 200 frame, the codes returns 4 all the time. But the result ie 4th frame don’t seem to be right. Where am I wrong ? Is my time_base conversion to actual frame faulty ?

  The test result using ffprobe

  Filename = test.mp4  
  
  Duration = 00:00:10.56 
  
  Fps = 25
  
  Total frames = 256   
  
  The key frames pkt_pts_time are at 2.120000  and 0.000000 (using -skip_frame nokey )
  
  Corresponding pkt_duration_time: 0.040000 and 0.040000 (  same, why?)

  Abstract of the code :

  // Objective: seek to the nearest key frame
  
  frameIndex = 200;
  
  int64_t timeBase = (int64_t(pCodecCtx->time_base.num) * AV_TIME_BASE) / int64_t(pCodecCtx->time_base.den);  
  
  int64_t seekTarget = int64_t(frameIndex) * timeBase;
  
  
  
  if (av_seek_frame(pFormatCtx, -1, seekTarget, AVSEEK_FLAG_FRAME | AVSEEK_FLAG_BACKWARD) < 0) return -1;
  
  
  
  //convert the time_base to actual frame
  
  auto time2frame = [&](int64_t tb) {
  
      return tb * int64_t(pCodecCtx->time_base.den) / (int64_t(pCodecCtx->time_base.num) * AV_TIME_BASE);
  
  };
  
  
  
  AVPacket avPacket;
  
  int result = av_read_frame(pFormatCtx, &avPacket);
  
  if (result == 0) {
  
  
  
      auto dts = avPacket.dts;
  
      auto pts = avPacket.pts;
  
      auto idx = avPacket.stream_index;
  
      auto f = time2frame(pts); // expecting the actual frame here
  
      std::cout << dts << pts << idx << f;
  
  }