Plugin Name: YouTube Embeddable Video
Plugin Description: Activate YouTube embeds and your readers will be able to share their favorite YouTube videos and beef up their responses right in the comment section.   
Plugin URL: http://youtube.com
Author: Jon
Author URL: https://www.intensedebate.com/people/jon
Date Added: March 5th, 2009

Code:
var id_youtube_plugin = {};
id_youtube_plugin.youtube_disabled_edit_ids = []; /* IntenseDebate commentid's that should have edit functionality disabled (contain youtube embeds) */
id_youtube_plugin.youtube_posted_from = 0; /* Which field should the poll embed code be inserted in (Reply or New Comment) */

/* add the YouTube button to the interface */
id_youtube_plugin.id_add_youtube_button = function() {
	id_add_plugin_button("javascript: id_youtube_plugin.id_show_youtube_embed(0)", "javascript: id_youtube_plugin.id_show_youtube_embed(1)", "//www.youtube.com/favicon.ico", "Add a YouTube Video", "YouTube", "Embed video");
	
	id_youtube_plugin.id_youtube_disable_edit_buttons();
};

/* display the popup for the url of the video to embed */
id_youtube_plugin.id_show_youtube_embed = function(posted_from) {
	/* keep track of if it was for a reply or a new comment */
	id_youtube_plugin.youtube_posted_from = posted_from;
	
	var link2 = $newEl('a');
	link2.href="javascript: id_youtube_plugin.id_add_youtube_embed_code();";
	IDReplaceHtml(link2, "<span></span><span class='idc-r'>Embed Video</span>");
	link2.className="idc-btn_s idc-disablestyles";
	link2.style.cssFloat = 'right';
	
	showMsgBox('Embed a YouTube Video', '<p>Enter the video URL to embed below:</p><input type="text" id="txtYouTubeURL"/>', 0, null, link2);
};

id_youtube_plugin.id_add_youtube_embed_code = function() {	
	/* Grab the url and identify the target textbox */
	var vidUrl = $id('txtYouTubeURL').value;
	
	/* make sure we add the embed code to the right textbox ( a reply or a new comment) */
	if(id_youtube_plugin.youtube_posted_from == 0)
		var textBox = $id('IDCommentNewThreadText');
	else
		var textBox = $id('txtComment');
	
	/* Check for valid match */
	var regex=/https?:\/\/([a-zA-Z0-9]+\.)?youtube\.com\/watch\?v=([A-Za-z0-9_&=-]*)/ig; 
	var m=regex.exec(vidUrl);
	
	/* If there is a match */
	if(m && m.length>2) {
		/* If no comment text has been entered yet be sure to clear the default stuff */
		if(textBox.value=='Enter text right here!') {
			textBox.value = '';
			textBox.style.color = 'black';
		}
				
		/* Add the embed code to the textbox */
		textBox.value += "[youtube " + m[2] + " " + m[0] + " youtube]";
		
		/* Hide the popup box */
		hideMsgBox();
		
		/* reset the regex */
		regex.lastIndex=0;
		
		/* Give focus to the text box */
		textBox.focus();
	}
	else
		/* Failed to match the url */
		alert('Unable to parse that url');
};

/* Disable the edit button for any comments that have a video */
id_youtube_plugin.id_youtube_disable_edit_buttons = function() {
	for(objElem in id_youtube_plugin.youtube_disabled_edit_ids) {		
		if($id('IDCommentPostReplyLinkEdit'+id_youtube_plugin.youtube_disabled_edit_ids[objElem]))
			$id('IDCommentPostReplyLinkEdit'+id_youtube_plugin.youtube_disabled_edit_ids[objElem]).style.display = 'none';	
	}
};

id_youtube_plugin.id_youtube_embed_replace = function(args) {
	var text = args['text'];
	
	//Check for valid match
	var youtube_regex=/\[youtube\s+([A-Za-z0-9_&=-]*)\s+(.*?)\s+youtube\]/ig;
	var m = youtube_regex.exec(text);

	//If there is a match
	if(m && m.length>1) {
		/* add the IntenseDebate commentid to the array of comments to disable editing for */
		id_youtube_plugin.youtube_disabled_edit_ids[id_youtube_plugin.youtube_disabled_edit_ids.length] = args['commentid'];
		
		/* reset the regex */
		youtube_regex.lastIndex=0;
		
		/* return the polldaddy div (where the poll will go */
		return text.replace(youtube_regex, '<div class="idc-video_youtube"><object width="480" height="295"><param name="movie" value="http://www.youtube.com/v/'+m[1]+'&hl=en&fs=1&rel=0"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="https://www.youtube.com/v/'+m[1]+'&hl=en&fs=1&rel=0" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="480" height="295"></embed></object></div>');
	}
	else {
		/* reset the regex */
		youtube_regex.lastIndex=0;
		return text;
	}
};

/* add filter to swap embed code */
/*id_add_filter('comment_text_load', function (args) { var text=args['text']; var newtext = text.replace(/\[youtube /ig, '<div class="idc-video_youtube"><object width="480" height="295"><param name="movie" value="http://www.youtube.com/v/zbLEtE4b-is&hl=en&fs=1&rel=0"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/'); if(newtext!=text) id_youtube_plugin.youtube_disabled_edit_ids[id_youtube_plugin.youtube_disabled_edit_ids.length] = args['commentid']; return newtext;});
id_add_filter('comment_text_load', function (args) { var text=args['text']; return text.replace(/(.*?)\syoutube\]/ig, '&hl=en&fs=1&rel=0" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="480" height="295"></embed></object></div>'); });*/

id_add_filter('comment_text_load', id_youtube_plugin.id_youtube_embed_replace);
id_add_action('idcomments_func_load',id_youtube_plugin.id_add_youtube_button); /* add youtube button on load */
id_add_action('user_login',id_youtube_plugin.id_youtube_disable_edit_buttons); /* disable edit buttons on login */
id_add_action('comment_post',id_youtube_plugin.id_youtube_disable_edit_buttons); /* disable edit buttons on comment post (for new comments w/ YouTube videos) */

CSS:
#idc-container .idc-video_youtube {
		        		clear: both;
		        		float: none;
		        		margin: 1em auto;
		        		width: 480px !important;
		        		}