TYPO3.Fluid

I've a model Tx_Mytube_Domain_Model_Video

I have created a ViewHelper
class Tx_Mytube_ViewHelpers_VideoViewHelper extends
Tx_Fluid_Core_ViewHelper_AbstractViewHelper {

• Renders the video player *
• @param Tx_Mytube_Domain_Model_Video $video
• @return string the content of the rendered TypoScript object
  */
  public function render(Tx_Mytube_Domain_Model_Video $video) {
  return "AAAAAA";
  }

}
?>

and a template

{namespace mytube=Tx_Mytube_ViewHelpers}
<mytube:video video="{video}"/>

But i having an exception

#1237900534: No validator found for argument name "video" with type
"Tx_Mytube_Domain_Model_Video" in view helper
"Tx_Mytube_ViewHelpers_VideoViewHelper".