Unnecessary gray background in Yandex browser background video?

Question

Browsers

There is a site business.egliens.ru
In all browsers, the background video is displayed as it should, and in the Yandex browser the background is gray.
How to remove this background?

Answer 1

so far it turned out to be corrected by the fact that I first set the webm format and then mp4
As I was told that the problem could be in the mp4 format,
but it's strange that it works in chrome anyway, and in Yandex with mp4 a gray background, although Yandex seems to be based on chrome.