YouTube Loop Playlist in the HTML
Loop Playlist in the HTML means that "the Video will start over again, every time it is finished". And If you want to play a YouTube video again and again then add loop & autoplay to the video tag; That means when it is used the video plays automatically, See the example below:
To have the video autoplay you'll need to add autoplay to the video tag as in the below syntax example:
Syntax example of Video tag with 'autoplay' & 'loop'
<video height="640" width="360" autoplay loop controls
<source src="Video_URL" type="video/mp4" >
</video>