ytdownload.tamper.js

// ==UserScript==
// @name       Youtube Download Video
// @namespace  http://www.strikeskids.com
// @version    0.05
// @description  Creates a download button on youtube videos to enable them to be downloaded
// @match	http*://*.youtube.com/watch*v=*
// @copyright  2014+, Strikeskids
// @require http://code.jquery.com/jquery-latest.js
// @run-at document-end
// @author Strikeskids
// ==/UserScript==

function parseUrlFmt(formatted) {
	var parts = formatted.split("&")
    var map = {}
    parts.forEach(function(part) {
        var sections = part.split('='),
            key = sections[0],
            value = decodeURIComponent(sections[1])
        map[key] = value
    })
    return map
}

function parseStreams() {
	var streams = ytplayer.config.args.url_encoded_fmt_stream_map.split(",")
    return streams.map(parseUrlFmt)
}

jQuery(function($) {
    var streams, select, link, container;
        
    container = $("#watch7-headline")
    
    select = $('<select/>', {
        on: {
            change: function(event) {
                link.attr('href', select.val())
            }
        }
    }).appendTo(container)
    
    parseStreams().forEach(function(stream) {
        $('<option/>', {
            value: stream.url,
            text: stream.quality + ' ' + stream.type.split(';')[0]
        }).appendTo(select)
    })
    
    link = $('<a/>', {
        href: select.val(),
        text: 'Download'
    }).appendTo(container)
});