How does Bing achieve its dynamic effect?

A few days ago, I saw the dynamic waterfall on the Bing homepage. When I wanted to see the implementation method, the effect was gone;

 

Today, I saw the dynamic fog Effect of Sequoia in California. I thought it was canvas, but I carefully watched that fog changed at every moment, rather than simply moving it, through network monitoring,

Found such a thing:

Http://s.cn.bing.net/az/hprichv/FoggyTrees_CorbisRM_711C566_005_ZH-CN.mp4

 

1.84 m,

There is a video tag in HTML, which is basically applicable to videos,

 

But this MP4 indeed Nb, 1.84 M, looks very clear, and the beginning and end are consistent, no frame jump! I guess it took a lot of effort to do it.