YouTube prevents hiding related videos using rel=0 as of September 2018.
However, you can work around this by using the YouTube Player API to show custom HTML instead of related videos.
Here is some example code that displays a custom "replay" button over the video once it completes, hiding the related videos:
<style>
#playerWrap {
display: inline-block;
position: relative;
}
#playerWrap.shown::after {
content:"";
position: absolute;
top: 0;
left: 0;
bottom: 0;
right: 0;
cursor: pointer;
background-color: black;
background-repeat: no-repeat;
background-position: center;
background-size: 64px 64px;
background-image: url(data:image/svg+xml;utf8;base64,PHN2ZyB4bWxucz0iaHR0cDovL3d3dy53My5vcmcvMjAwMC9zdmciIHdpZHRoPSIxMjgiIGhlaWdodD0iMTI4IiB2aWV3Qm94PSIwIDAgNTEwIDUxMCI+PHBhdGggZD0iTTI1NSAxMDJWMEwxMjcuNSAxMjcuNSAyNTUgMjU1VjE1M2M4NC4xNSAwIDE1MyA2OC44NSAxNTMgMTUzcy02OC44NSAxNTMtMTUzIDE1My0xNTMtNjguODUtMTUzLTE1M0g1MWMwIDExMi4yIDkxLjggMjA0IDIwNCAyMDRzMjA0LTkxLjggMjA0LTIwNC05MS44LTIwNC0yMDQtMjA0eiIgZmlsbD0iI0ZGRiIvPjwvc3ZnPg==);
}
</style>
<div>
<div id="playerWrap">
<iframe
width="640" height="360"
src="https://www.youtube.com/embed/0sDg2h3M1RE?enablejsapi=1"
frameborder="0"
></iframe>
</div>
</div>
<script>
var playerFrame = document.currentScript.previousElementSibling.children[0].children[0];
var tag = document.createElement('script');
tag.src = "https://www.youtube.com/iframe_api";
var firstScriptTag = document.getElementsByTagName('script')[0];
firstScriptTag.parentNode.insertBefore(tag, firstScriptTag);
var player;
function onYouTubeIframeAPIReady() {
player = new YT.Player(playerFrame, {
videoId: 'M7lc1UVf-VE',
events: {
'onStateChange': onPlayerStateChange
}
});
}
function onPlayerStateChange(event) {
if (event.data == YT.PlayerState.ENDED) {
document.getElementById("playerWrap").classList.add("shown");
}
}
document.getElementById("playerWrap").addEventListener("click", function() {
player.seekTo(0);
document.getElementById("playerWrap").classList.remove("shown");
});
</script>
For the most up-to-date code, including the minified version, description, demo, and instructions, view my blog post on the subject.
