Show youtube embed as width 100%

youtube_iframe_to_width100percent.php

<?php
$youtube_url = 'https://www.youtube.com/watch?v=UeR_jEx6Pzs';
// or
$youtube_url = '<iframe width="560" height="315" src="https://www.youtube.com/embed/UeR_jEx6Pzs" frameborder="0" allowfullscreen></iframe>';
if ($youtube_url) {
  if (preg_match('/iframe/', $youtube_url)) {
    $iframe_url = preg_replace('/width=[\"\'].*?[\"\']/', 'width="100%"', $youtube_url);
    $iframe_url = preg_replace('/height=[\"\'].*?[\"\']/', 'height="100%"', $iframe_url);
    $fixed = $iframe_url;
  }
  else {
    $video_id = preg_replace("/.*?[\&\?]v=([a-zA-Z0-9_]+)?.*/", "$1", $youtube_url);
    $fixed = '<iframe width="100%" height="100%" src="https://www.youtube.com/embed/' . $video_id . '" frameborder="0" allowfullscreen></iframe>';
  }
}

print $fixed;

youtube_width_100percent.scss

.youtube-wrapper {
    position: relative;
    width: 100%;
    height: 0;
    padding-bottom: 56.25%;
    margin: 0 0 15px;

    iframe {
        position: absolute;
        width: 100%;
        height: 100%;
        left: 0;
        top: 0;
    }
}