Getting thumbnail when post uses shortcodes for video

Hi,

I’m using a custom plugin to add youtube videos to my blog. Basically the shortcode that goes into the post looks something like this:

[youtube id=”RLZUKqpXYzU” width=”600″ height=”340″ position=”left”]

but when the post is displayed on the post page it looks like this:

<iframe class=”youtube-video left” id=”player” video-id=”RLZUKqpXYzU” frameborder=”0″ allowfullscreen=”1″ title=”YouTube video player” width=”1000″ height=”450″ src=”https://www.youtube.com/embed/RLZUKqpXYzU?enablejsapi=1&controls=1&showinfo=0&color=red&rel=0&wmode=transparent&modestbranding=1&theme=dark&origin=http%3A%2F%2Fyiral.com”></iframe&gt;

With the default settings this plugin does not seem to get the thumbnail. Please could you tell me what setting I need to change to make it function?

Thank you.

https://ww.wp.xz.cn/plugins/video-thumbnails/