$this->addOption('mime_type_guessers', array(
      array($this, 'guessFromFileinfo'),
      array($this, 'guessFromMimeContentType'),
      array($this, 'guessFromFileBinary'),
    ));


//

  $this->validatorSchema['video']->setOption('mime_type_guessers', array(
    array($this->validatorSchema['video'], 'guessFromFileBinary')
  ));