http://www.sitepoint.com/forums/showthread.php?1212490-how-with-JavaScript-amp-jQuery-or-PHP-get-media-file-duration-eg-video-mp4
No-Library (pure JS), HTML, CSS, JavaScript
jQuery 1.9.1, HTML, CSS, JavaScript
plain count up timer in javascript
jQuery 3.4.1, HTML, CSS, JavaScript
jQuery 3.2.1, HTML, CSS, JavaScript
Por defecto, el responsive menu de bootstrap no se oculta al ser clickeado, por eso hay que agregar dos atributos a los anchors <a></a>