Method getParameterSets

YUViewLib/src/filesource/FileSourceFFmpegFile.cpp:219–333

}

QList<QByteArray> FileSourceFFmpegFile::getParameterSets()
{
  if (!this->isFileOpened)
    return {};

  /* The SPS/PPS are somewhere else in containers:
   * In mp4-container (mkv also) PPS/SPS are stored separate from frame data in global headers.
   * To access them from libav* APIs you need to look for extradata field in AVCodecContext of
   * AVStream which relate to needed video stream. Also extradata can have different format from
   * standard H.264 NALs so look in MP4-container specs for format description. */
  const auto extradata = this->getExtradata();
  if (extradata.isEmpty())
  {
    DEBUG_FFMPEG("Error no extradata could be found.");
    return {};
  }

  QList<QByteArray> retArray;

  // Since the FFmpeg developers don't want to make it too easy, the extradata is organized
  // differently depending on the codec.
  auto codecID = this->ff.getCodecIDWrapper(video_stream.getCodecID());
  if (codecID.isHEVC())
  {
    if (extradata.at(0) == 1)
    {
      // Internally, ffmpeg uses a custom format for the parameter sets (hvcC).
      // The hvcC parameters come first, and afterwards, the "normal" parameter sets are sent.

      // The first 22 bytes are fixed hvcC parameter set (see hvcc_write in libavformat hevc.c)
      auto numOfArrays = int(extradata.at(22));

      int pos = 23;
      for (int i = 0; i < numOfArrays; i++)
      {
        // The first byte contains the NAL unit type (which we don't use here).
        pos++;
        // int byte = (unsigned char)(extradata.at(pos++));
        // bool array_completeness = byte & (1 << 7);
        // int nalUnitType = byte & 0x3f;

        // Two bytes numNalus
        int numNalus = (unsigned char)(extradata.at(pos++)) << 7;
        numNalus += (unsigned char)(extradata.at(pos++));

        for (int j = 0; j < numNalus; j++)
        {
          // Two bytes nalUnitLength
          int nalUnitLength = (unsigned char)(extradata.at(pos++)) << 7;
          nalUnitLength += (unsigned char)(extradata.at(pos++));

          // nalUnitLength bytes payload of the NAL unit
          // This payload includes the NAL unit header
          auto rawNAL = extradata.mid(pos, nalUnitLength);
          retArray.append(rawNAL);
          pos += nalUnitLength;
        }
      }