How to get a YouTube thumbnail from a YouTube iframe?

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For instance I have a blog post that has the following iframe.
</script>
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                <span>2021-01-30 09:22</span>
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<p>This function work with all types of youtube links &amp; domains such as <br />
https://www.youtube.com/watch?v=WZKW2Hq2fks</p>
<p>https://youtu.be/WZKW2Hq2fks</p>
<p>https://www.youtube.com/embed/WZKW2Hq2fks&nbsp;</p>
<p>https://youtu.be/WZKW2Hq2fks?t=66</p>
<p>And you can get the quality you want.</p>
<p>To use it:</p>
<pre><code>// quality options: low, medium, high, max | default is max.
var thumbnail = get_youtube_thumbnail('https://youtu.be/WZKW2Hq2fks', 'max');
console.log(thumbnail);
</code></pre>
<hr />
<pre><code>function get_youtube_thumbnail(url, quality){
    if(url){
        var video_id, thumbnail, result;
        if(result = url.match(/youtube\.com.*(\?v=|\/embed\/)(.{11})/))
        {
            video_id = result.pop();
        }
        else if(result = url.match(/youtu.be\/(.{11})/))
        {
            video_id = result.pop();
        }

        if(video_id){
            if(typeof quality == &quot;undefined&quot;){
                quality = 'high';
            }
        
            var quality_key = 'maxresdefault'; // Max quality
            if(quality == 'low'){
                quality_key = 'sddefault';
            }else if(quality == 'medium'){
                quality_key = 'mqdefault';
            } else if (quality == 'high') {
                quality_key = 'hqdefault';
            }

            var thumbnail = &quot;http://img.youtube.com/vi/&quot;+video_id+&quot;/&quot;+quality_key+&quot;.jpg&quot;;
            return thumbnail;
        }
    }
    return false;
}
</code></pre>
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                <span>2021-01-30 09:36</span>
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<p><strong>YouTube thumbnails</strong></p>

<p>YouTube thumbnails can be found in this standard path:</p>

<pre class="lang-none prettyprint-override"><code>http://img.youtube.com/vi/[video-id]/[thumbnail-number].jpg
</code></pre>

<ul>
<li><code>[video-id]</code> is the YouTube video ID, e.g. <code>1sIWez9HAbA</code>.</li>
<li><code>[thumbnail-number]</code> is the number of the thumbnail of the 4 each
video usually has, e.g. <code>0</code>.</li>
</ul>

<p><strong>Getting the thumbnail from an iframe</strong></p>

<p>So, based on the <code>iframe</code>'s <code>src</code> attribute you may construct the URL of the thumbnail directly.</p>

<p>For example, using jQuery:</p>

<pre><code>var iframe           = $('iframe:first');
var iframe_src       = iframe.attr('src');
var youtube_video_id = iframe_src.match(/youtube\.com.*(\?v=|\/embed\/)(.{11})/).pop();

if (youtube_video_id.length == 11) {
    var video_thumbnail = $('&lt;img src="//img.youtube.com/vi/'+youtube_video_id+'/0.jpg"&gt;');
    $(body).append(video_thumbnail);
}
</code></pre>

<p>Note this example checks the URL of the <code>iframe</code> for a valid YouTube video ID and assumes it to be 11 characters long, which is the de facto standard.</p>

<h2>See jsFiddle Demo</h2>
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<p><strong>Get Youtube thumbnail images using below urls</strong></p>

<p><strong>Low quality</strong></p>

<pre><code> https://img.youtube.com/vi/[video-id]/sddefault.jpg
</code></pre>

<p><strong>medium quality</strong></p>

<pre><code> https://img.youtube.com/vi/[video-id]/mqdefault.jpg
</code></pre>

<p><strong>High quality</strong></p>

<pre><code>http://img.youtube.com/vi/[video-id]/hqdefault.jpg
</code></pre>

<p><strong>maximum resolution</strong></p>

<pre><code>http://img.youtube.com/vi/[video-id]/maxresdefault.jpg
</code></pre>

<p>example: https://img.youtube.com/vi/OYr-KPboPDw/hqdefault.jpg</p>
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