Simplepie plugin processing resize video

I use the blog style full option and i wanted to resize the video in the rss feed a load. I write a php code to resize all videos to fit my WordPress template, some was just to big or to small.
here the code

<?php

/**
 * EMBED RESIZING
 *
 * This will let you resize all videos in a rss feed.
 *
 * If you don't want to do anything to the content, simply remove the function.
 */

// We MUST keep this classname.
class SimplePie_PostProcess
{
	// Function name MUST be the same as the template tag we're processing, all lowercase, and MUST accept a single string parameter.
	function item_content($s)
	{
		// Match all images in the content.
		// I would recommend the regex tool at http://osteele.com/tools/rework/ to do testing ahead of time.
		if (preg_match('#(<(object)(.+?)</object>)#is',$s,$matches)) {

		$embedcode = $matches[1];
		$embedcode = str_replace("\\", "", $embedcode);
		$embedcode = preg_replace('/width=(\'|\")(.*?)(\'|\")/', 'width="550"', $embedcode); #385
		$embedcode = preg_replace('/height=(\'|\")(.*?)(\'|\")/', 'height="400"', $embedcode); #300
		$s = preg_replace('#(<(object)(.+?)</object>)#is', $embedcode, $s);
		}

		// Return $s back out to the plugin.
		return $s;
	}
}

?>

i called this file embed.php and put it in the simplepie-plugin-for-wordpress plugin folder. You can choose the option in the simplepie admin section Content “Post-Processing Rules:”