Just add the YouTube video ID to the 'video-id' data attribute

HTML

<div class="youtube_video_lazy_load"
    data-video-id="AddYouTubeVideoIdHere"
    data-iframe-width="853"
    data-iframe-height="480"
    data-iframe-src-url-vars="rel=0&showinfo=0&&mute=1&disablekb=1">
</div>

JavaScript

var youtube_videos_loaded = 0;
        function loadYoutubeVideos() {
            $('.youtube_video_lazy_load').each(function () {

                if (youtube_videos_loaded == 0) {
                    var videoID = $(this).data("video-id");
                    var iframeWidth = $(this).data("iframe-width");
                    var iframeHeight = $(this).data("iframe-height");
                    var iframeSrcVars = $(this).data("iframe-src-url-vars");

                    if (videoID) {
                        var iframe = document.createElement("iframe");
                        iframe.setAttribute("frameborder", "0");
                        iframe.setAttribute("allowfullscreen", "");
                        iframe.setAttribute("src", "https://www.youtube.com/embed/" + videoID + "?" + iframeSrcVars);
                        iframe.setAttribute("width", iframeWidth);
                        iframe.setAttribute("height", iframeHeight);
                        /*iframe.setAttribute("allow", "accelerometer; encrypted - media; gyroscope; picture - in -picture");*/
                        $(this).html(iframe);
                    }

                }

            });

            youtube_videos_loaded = 1;
        }

    var lastScrollTop = 0;
    $(window).scroll(function (event) {
        var st = $(this).scrollTop();
        if (st > lastScrollTop) {
            loadYoutubeVideos();
        } else {
            // up scroll code
        }
        lastScrollTop = st;
    });