Add &rel=0 to Youtube oembed videos

functions.php

<?php
/**
     * Filter YouTube oEmbed to include '&rel=0' to force channel related videos
     * once video is complete, rather than showing user related videos.
     *
     * @param $html
     * @param $url
     * @param $args
     *
     * @return mixed
     */
    public function youtubeOembedSrcAdjust( $html, $url, $args ) {
        return str_replace( '?feature=oembed', '?feature=oembed&rel=0', $html );
    }
add_filter( 'oembed_result', 'youtubeOembedSrcAdjust', 10, 3 );