long VideoTrack::Parse(Segment* pSegment, const Info& info,
                       long long element_start, long long element_size,
                       VideoTrack*& pResult) {
  if (pResult)
    return -1;

  if (info.type != Track::kVideo)
    return -1;

  long long width = 0;
  long long height = 0;
  long long display_width = 0;
  long long display_height = 0;
  long long display_unit = 0;
  long long stereo_mode = 0;

  double rate = 0.0;

  IMkvReader* const pReader = pSegment->m_pReader;

  const Settings& s = info.settings;
  assert(s.start >= 0);
  assert(s.size >= 0);

  long long pos = s.start;
  assert(pos >= 0);

  const long long stop = pos + s.size;

  Colour* colour = NULL;
  Projection* projection = NULL;

  while (pos < stop) {
    long long id, size;

    const long status = ParseElementHeader(pReader, pos, stop, id, size);

    if (status < 0)  // error
      return status;

    if (id == libwebm::kMkvPixelWidth) {
      width = UnserializeUInt(pReader, pos, size);

      if (width <= 0)
        return E_FILE_FORMAT_INVALID;
    } else if (id == libwebm::kMkvPixelHeight) {
      height = UnserializeUInt(pReader, pos, size);

      if (height <= 0)
        return E_FILE_FORMAT_INVALID;
    } else if (id == libwebm::kMkvDisplayWidth) {
      display_width = UnserializeUInt(pReader, pos, size);

      if (display_width <= 0)
        return E_FILE_FORMAT_INVALID;
    } else if (id == libwebm::kMkvDisplayHeight) {
      display_height = UnserializeUInt(pReader, pos, size);

      if (display_height <= 0)
        return E_FILE_FORMAT_INVALID;
    } else if (id == libwebm::kMkvDisplayUnit) {
      display_unit = UnserializeUInt(pReader, pos, size);

      if (display_unit < 0)
        return E_FILE_FORMAT_INVALID;
    } else if (id == libwebm::kMkvStereoMode) {
      stereo_mode = UnserializeUInt(pReader, pos, size);

      if (stereo_mode < 0)
        return E_FILE_FORMAT_INVALID;
    } else if (id == libwebm::kMkvFrameRate) {
      const long status = UnserializeFloat(pReader, pos, size, rate);

      if (status < 0)
        return status;

      if (rate <= 0)
        return E_FILE_FORMAT_INVALID;
    } else if (id == libwebm::kMkvColour) {
      if (!Colour::Parse(pReader, pos, size, &colour))
        return E_FILE_FORMAT_INVALID;
    } else if (id == libwebm::kMkvProjection) {
      if (!Projection::Parse(pReader, pos, size, &projection))
        return E_FILE_FORMAT_INVALID;
    }

    pos += size;  // consume payload
    if (pos > stop)
      return E_FILE_FORMAT_INVALID;
  }

  if (pos != stop)
    return E_FILE_FORMAT_INVALID;

  VideoTrack* const pTrack =
      new (std::nothrow) VideoTrack(pSegment, element_start, element_size);

  if (pTrack == NULL)
    return -1;  // generic error

  const int status = info.Copy(pTrack->m_info);

  if (status) {  // error
    delete pTrack;
    return status;
  }

  pTrack->m_width = width;
  pTrack->m_height = height;
  pTrack->m_display_width = display_width;
  pTrack->m_display_height = display_height;
  pTrack->m_display_unit = display_unit;
  pTrack->m_stereo_mode = stereo_mode;
  pTrack->m_rate = rate;
  pTrack->m_colour = colour;
  pTrack->m_projection = projection;

  pResult = pTrack;
  return 0;  // success
}