intersect the viewport

intersect the viewport

[1] Allow delaying autoplay until video elements become visible ( (Zhiqiang Zhang著, )) <https://github.com/whatwg/html/commit/8ebd581ea848c476368e5f25ee3a3c31803b29fa>

[2] Allow delaying autoplay until video elements become visible ( (Zhiqiang Zhang著, )) <https://github.com/whatwg/html/commit/8ebd581ea848c476368e5f25ee3a3c31803b29fa>