HTML

youtube autoplay video

<!--note: add &autoplay=1 to src and add property allow="autoplay" -->
<iframe
 src="https://www.youtube.com/embed/lw3p6VqC-zI?&autoplay=1"
 allow="autoplay"
 >
 </iframe>

autoplay youtube video

// Add this to your URL
?autoplay=1&mute=1
// example
https://www.youtube.com/embed/9QTojZVR_Ec?autoplay=1&mute=1

Youtube autoplay

Add: ?autoplay=1&mute=1 to the ened of the video, like this:
<iframe src="https://www.youtube-nocookie.com/embed/IO9XlQrEt2Y?autoplay=1&mute=1">...