gistfile1.php

<?php

function valid_youtube($string)
{
	return TRUE;
}


function valid_stream($link, $providers)
{	
	// If you set a simple string 
	$providers = (array) $providers;

	// Loop all providers
	foreach ($providers as $provider)
	{
		if (function_exists('valid_' . $provider))
		{
			$callback = 'valid_' . $provider;

			if ($callback($link))
			{
				return TRUE;
			}
		}
	}

	return FALSE;
}

var_dump(valid_stream('http://www.youtube.com/', array('dailymotion', 'youtube')));

?>