this code block pauses youtube videos on scroll when videos are disappeared from window.

 var tag = document.createElement('script');
tag.src = "//www.youtube.com/player_api";
var firstScriptTag = document.getElementsByTagName('script')[0];
firstScriptTag.parentNode.insertBefore(tag, firstScriptTag);

var youtubePlayers = new Array();
function onYouTubeIframeAPIReady() {

    var counter = 0;
    $(".youtube-video").each(function () {
        counter  ;
        var id = $(this).attr("id");
        var onlineId = $(this).attr("data-online-id");

        var playerInfo = {
            id: id,
            //height: '390',
            //width: '640',
            videoId: onlineId
        };

        var curplayer = createPlayer(playerInfo);
        youtubePlayers[counter] = curplayer;
    });
}

function createPlayer(playerInfo) {
    return new YT.Player(playerInfo.id, {
        height: playerInfo.height,
        width: playerInfo.width,
        videoId: playerInfo.videoId,
    });
} 

 $(document).ready(function () {

    $(window).scroll(function () {

          $(".youtube-video").each(function () {
            var isOnScreen = $(this).isOnScreen();

                if (!isOnScreen) {

                    var playerId = $(this).attr("id");

                    $(youtubePlayers).each(function (i, obj) {

                        if (obj != undefined && obj.pauseVideo) {

                            if (obj.a.id == playerId) {
                                obj.pauseVideo();
                            }
                        }
                    });
                }
        });

    });
});