code: public function addEnclosure($strFile, $strUrl=null, $strMedia='enclosure')
  	{
  		if ($strFile == '' || !file_exists(System::getContainer()->getParameter('kernel.project_dir') . '/' . $strFile))
  		{
  			return;
  		}
  
  		if ($strUrl === null)
  		{
  			$strUrl = Environment::get('base');
  		}
  
  		$objFile = new File($strFile);
  
  		$this->arrData['enclosure'][] = array
  		(
  			'media' => $strMedia,
  			'url' => $strUrl . System::urlEncode($strFile),
  			'length' => $objFile->size,
  			'type' => $objFile->mime
  		);
  	}
docs: Add an enclosure
  
  @param string $strFile  The file path
  @param string $strUrl   The base URL
  @param string $strMedia The media type