Where alpha is a requirement, this is very clever.

However, in many cases, the requirement isn't actually transparency, the requirement is a video background seamless with the containing page.

With most pages white or off-white, this can be done at production. Even responsive dark mode can be done in production if two clips are made.

We used this simpler technique for borderless animated video (e.g., a streaming video spokesperson walking across your e-commerce product page) 20 years ago.

The optical illusion of borderless transparency works so surprisingly well it's unbelievable it's not seen widely.