YouTube videos aren’t responsive by default. To make your YouTube Videos responsive, you can use the below snippet of code. Replace the “src=” with the output from the YouTube Video page like the examples below:
16:9 aspect ratio
<div class="embed-responsive embed-responsive-16by9"><iframe allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture"allowfullscreen=""frameborder="0"height="315"src="https://www.youtube.com/embed/DHRBw5XNnVE"width="560"></iframe></div>
4:3 aspect ratio
<div class="embed-responsive embed-responsive-4by3"><iframe allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture"allowfullscreen=""frameborder="0"height="315"src="https://www.youtube.com/embed/DHRBw5XNnVE"width="560"></iframe></div>