window.onload = function() {
    var vidid = document.getElementById("video-1");
    vidid.innerHTML = "<iframe style='padding: 0; margin: 0; border: 0; width: 100%; height: 100%;' scrolling='no' src='http://player.twitch.tv/?branding=false&showInfo=false&html5&channel=" + window.location.pathname.substr(1) + "'></iframe>";
};

Code above should work in the latest versions of firefox (with mse/h.264 enabled) and chrome/ium if you don't have flash installed or have flash disabled. Haven't tested with flash.