Resizing element to parent div

1) CSS only

Demo

HTML

<div class="wrapper">
  <video class="videoInsert">
  <source src="http://www.w3schools.com/html/movie.mp4" type="video/mp4">
  <source src="movie.ogg" type="video/ogg">
  Your browser does not support the video tag.
 </video>
</div>

css

.videoInsert {
    position: absolute; 
    right: 0; 
    bottom: 0;
    min-width: 100%; 
    min-height: 100%;
    width: auto; 
    height: auto; 
    z-index: -100;
    background-size: cover;
    overflow: hidden;
}

2) jQuery

Demo

HTML

<div id="video-viewport">
    <video autoplay preload width="640" height="360">
        <source src="https://s3.amazonaws.com/whiteboard.is/videos/bg-loop-new.mp4" />
    </video>
</div>

css

#video-viewport {
    position: absolute;
    top: 0;
    left:0;
    overflow: hidden;
    z-index: -1; /* for accessing the video by click */
}
body{
    margin:0;
}

jquery

from this answer – simulate background-size:cover on <video> or <img>

var min_w = 300; // minimum video width allowed
var vid_w_orig;  // original video dimensions
var vid_h_orig;

jQuery(function() { // runs after DOM has loaded

    vid_w_orig = parseInt(jQuery('video').attr('width'));
    vid_h_orig = parseInt(jQuery('video').attr('height'));
    $('#debug').append("<p>DOM loaded</p>");

    jQuery(window).resize(function () { resizeToCover(); });
    jQuery(window).trigger('resize');
});

function resizeToCover() {

    // set the video viewport to the window size
    jQuery('#video-viewport').width(jQuery(window).width());
    jQuery('#video-viewport').height(jQuery(window).height());

    // use largest scale factor of horizontal/vertical
    var scale_h = jQuery(window).width() / vid_w_orig;
    var scale_v = jQuery(window).height() / vid_h_orig;
    var scale = scale_h > scale_v ? scale_h : scale_v;

    // don't allow scaled width < minimum video width
    if (scale * vid_w_orig < min_w) {scale = min_w / vid_w_orig;};

    // now scale the video
    jQuery('video').width(scale * vid_w_orig);
    jQuery('video').height(scale * vid_h_orig);
    // and center it by scrolling the video viewport
    jQuery('#video-viewport').scrollLeft((jQuery('video').width() - jQuery(window).width()) / 2);
    jQuery('#video-viewport').scrollTop((jQuery('video').height() - jQuery(window).height()) / 2);
};

3) using iframe css only

Demo

HTML

<div class="wrapper">
    <div class="h_iframe">
        <iframe src="https://www.youtube.com/embed/9KunP3sZyI0" frameborder="0" allowfullscreen></iframe>
    </div>
</div>

css

.h_iframe iframe {
  position:absolute;
  top:0;
  left:0;
  width:100%; 
  height:100%;
}