class Box {}

Source

class Box {
  public $size; // In bytes.
  public $type; // Four characters.
  public $version; // 0 or actual version if this is a full box.
  public $flags; // 0 or actual value if this is a full box.
  public $content_size; // 'size' minus the header size.

  /**
   * Reads the box header.
   *
   * @param stream  $handle              The resource the header will be parsed from.
   * @param int     $num_parsed_boxes    The total number of parsed boxes. Prevents timeouts.
   * @param int     $num_remaining_bytes The number of bytes that should be available from the resource.
   * @return Status                      FOUND on success or an error on failure.
   */
  public function parse( $handle, &$num_parsed_boxes, $num_remaining_bytes = MAX_SIZE ) {
    // See ISO/IEC 14496-12:2012(E) 4.2
    $header_size = 8; // box 32b size + 32b type (at least)
    if ( $header_size > $num_remaining_bytes ) {
      return INVALID;
    }
    if ( !( $data = read( $handle, 8 ) ) ) {
      return TRUNCATED;
    }
    $this->size = read_big_endian( $data, 4 );
    $this->type = substr( $data, 4, 4 );
    // 'box->size==1' means 64-bit size should be read after the box type.
    // 'box->size==0' means this box extends to all remaining bytes.
    if ( $this->size == 1 ) {
      $header_size += 8;
      if ( $header_size > $num_remaining_bytes ) {
        return INVALID;
      }
      if ( !( $data = read( $handle, 8 ) ) ) {
        return TRUNCATED;
      }
      // Stop the parsing if any box has a size greater than 4GB.
      if ( read_big_endian( $data, 4 ) != 0 ) {
        return ABORTED;
      }
      // Read the 32 least-significant bits.
      $this->size = read_big_endian( substr( $data, 4, 4 ), 4 );
    } else if ( $this->size == 0 ) {
      $this->size = $num_remaining_bytes;
    }
    if ( $this->size < $header_size ) {
      return INVALID;
    }
    if ( $this->size > $num_remaining_bytes ) {
      return INVALID;
    }

    $has_fullbox_header = $this->type == 'meta' || $this->type == 'pitm' ||
                          $this->type == 'ipma' || $this->type == 'ispe' ||
                          $this->type == 'pixi' || $this->type == 'iref' ||
                          $this->type == 'auxC';
    if ( $has_fullbox_header ) {
      $header_size += 4;
    }
    if ( $this->size < $header_size ) {
      return INVALID;
    }
    $this->content_size = $this->size - $header_size;
    // Avoid timeouts. The maximum number of parsed boxes is arbitrary.
    ++$num_parsed_boxes;
    if ( $num_parsed_boxes >= MAX_NUM_BOXES ) {
      return ABORTED;
    }

    $this->version = 0;
    $this->flags   = 0;
    if ( $has_fullbox_header ) {
      if ( !( $data = read( $handle, 4 ) ) ) {
        return TRUNCATED;
      }
      $this->version = read_big_endian( $data, 1 );
      $this->flags   = read_big_endian( substr( $data, 1, 3 ), 3 );
      // See AV1 Image File Format (AVIF) 8.1
      // at https://aomediacodec.github.io/av1-avif/#avif-boxes (available when
      // https://github.com/AOMediaCodec/av1-avif/pull/170 is merged).
      $is_parsable = ( $this->type == 'meta' && $this->version <= 0 ) ||
                     ( $this->type == 'pitm' && $this->version <= 1 ) ||
                     ( $this->type == 'ipma' && $this->version <= 1 ) ||
                     ( $this->type == 'ispe' && $this->version <= 0 ) ||
                     ( $this->type == 'pixi' && $this->version <= 0 ) ||
                     ( $this->type == 'iref' && $this->version <= 1 ) ||
                     ( $this->type == 'auxC' && $this->version <= 0 );
      // Instead of considering this file as invalid, skip unparsable boxes.
      if ( !$is_parsable ) {
        $this->type = 'unknownversion';
      }
    }
    // print_r( $this ); // Uncomment to print all boxes.
    return FOUND;
  }
}

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