An attempt at making a bookmarklet to download any YouTube and/or MP4 videos on a page.

video-dl-bookmarklet.js

(function() {
	var appName = "";

	var jQueryVersion = "2.0.3";
	var jQueryUIVersion = "1.10.3";
	var jQueryUITheme = "redmond";

	function loadPrerequisites(callback)
	{
		loadJQuery(function() {
			loadJQueryUI(function() {
				callback();
			});
		});
	}

	function loadJQuery(callback)
	{
		if (window.jQuery === undefined || window.jQuery.fn.jquery < jQueryVersion)
		{
			var done = false;
			var script = document.createElement("script");
			script.src = "http://ajax.googleapis.com/ajax/libs/jquery/" + jQueryVersion + "/jquery.min.js";
			script.onload = script.onreadystatechange = function() {
				if (!done && (!this.readyState || this.readyState == "loaded" || this.readyState == "complete"))
				{
					done = true;
					callback();
				}
			};
			document.getElementsByTagName("head")[0].appendChild(script);
		}
		else
		{
			callback();
		}
	}

	function loadJQueryUI(callback)
	{
		var cssURL = "https://ajax.googleapis.com/ajax/libs/jqueryui/" + jQueryUIVersion + "/themes/" + jQueryUITheme + "/jquery-ui.min.css";
		$('head').append("<link rel='stylesheet' href='" + cssURL  + "' type='text/css' />");

		if ($.ui === undefined || $.ui.version < jQueryUIVersion)
		{
			var script = "http://ajax.googleapis.com/ajax/libs/jqueryui/" + jQueryUIVersion + "/jquery-ui.min.js";
			$.getScript(script, function(data, textStatus, jqxhr) {
				callback();
			});
		}
		else
		{
			callback();
		}
	}
	
	function initMyBookmarklet()
	{
		(window.myBookmarklet = function() {
			video_links = getMP4VideoLinks();

			if (video_links.length == 0)
			{
				showDialog("video-dialog", "No Videos Found", "Sorry! No videos were found.", ["OK"], [function() { $(this).dialog("close"); }]);
			}
			else
			{
				video_links.push("Cancel");
				actions = [];

				for (var i = 0; i < video_links.length; i++)
				{
					actions.push(function() { $(this).dialog("close"); });
				}
				
				showDialog("video-dialog", "Select a Video", "Please select a video to download.", video_links, actions);
			}
		})();
	}

	function getMP4VideoLinks()
	{
		var link_strings = [], links = document.links;
		for (var i = 0; i < links.length; i++)
		{
			if (links[i].href.match(/\.mp4$/i))
			{
				link_strings.push(links[i].href);
			}
		}
		return link_strings;
	}

	function showDialog(id, title, text, buttons, callbacks)
	{
		hid = "#" + id;

		if ($(hid).length == 0)
		{
			var html = "\
				<div id='" + id + "' title='" + title + "'>\
				<p>" + text  + "</p>\
				</div>";
			$("body").append(html);
			//$("div").css("visibility", "hidden");
		}

		var buttonsObject = new Object();
		for (var i = 0; i < buttons.length; i++)
		{
			buttonsObject[buttons[i]] = callbacks[i];
		}

		$(hid).dialog({
			resizable:false,
			width:200,
			height:140,
			modal:true,
			buttons:buttonsObject
		});
	}

	loadPrerequisites(initMyBookmarklet);
})();