Here's how to do it in Squarespace using the embed block classes to create responsiveness.
Put this into a code block:
<div class="sqs-block embed-block sqs-block-embed" data-block-type="22" >
<div class="sqs-block-content"><div class="intrinsic" style="max-width:100%">
<div class="embed-block-wrapper embed-block-provider-YouTube" style="padding-bottom:56.20609%;">
<iframe allow="autoplay; fullscreen" scrolling="no" data-image-dimensions="854x480" allowfullscreen="true" src="https://www.youtube.com/embed/live_stream?channel=CHANNEL_ID_HERE" width="854" data-embed="true" frameborder="0" title="YouTube embed" class="embedly-embed" height="480">
</iframe>
</div>
</div>
</div>
Tweak however you'd like!