public function wp_calculate_image_srcset( $sources, $size_array, $image_src, $image_meta, $attachment_id ) {
		foreach ( $sources as $width => $source ) {
			$size   = $this->find_image_size_from_width( $image_meta['sizes'], $width );
			$OS_url = $this->swift_get_attachment_url( $attachment_id, null, $size );
			if ( false === $OS_url || is_wp_error( $OS_url ) ) {
				continue;
			}
			$sources[ $width ]['url'] = $OS_url;
		}
		return $sources;
	}