var videos = [
    '1',
    '2',
    '3',
    '4',
    '5',
    '6'
];

var index = Math.floor(Math.random() * videos.length);
var html = '<div class="pmeme"><video id="video" autoplay="autoplay" loop="loop" onloadstart="this.volume=0.2">' + videos[index] + '</video></div>';
document.write(html);