<div id="mioModalVideo" class="modal fade">
        <div class="modal-dialog">
            <div class="modal-content">
                <div class="modal-header">
                    <h5 class="modal-title">Mio Video</h5>
                    <button type="button" class="close" data-dismiss="modal">&times;</button>
                </div>
                <div class="modal-body">
                  <div class="embed-responsive embed-responsive-16by9">
                    <iframe id="unBelVideo" class="embed-responsive-item" width="560" height="315" src="https://www.youtube.com/embed/WmVLcj-XKnM" allowfullscreen></iframe>
                  </div>
                </div>
            </div>
        </div>
    </div>

$(document).ready(function(){
    var url = $("#unBelVideo").attr('src');
    $("#mioModalVideo").on('hide.bs.modal', function(){
        $("#unBelVideo").attr('src', '');
    });  
    $("#mioModalVideo").on('show.bs.modal', function(){
        $("#unBelVideo").attr('src', url);
    });
});