'Autoplay Youtube video with sound on?

I have been looking all over the place and never found an answer to this question.

It's either you have autoplay and no sound. Or with sound but without autoplay.

However, I found this site where you click play it opens a box and YT video autoplay with sound.

I thought it's impossible. But this site somehow did it.

Can anyone explain how they did that?

And please don't delete this thread, many people are searching for this.

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