When you checkout the HTML from x.com for a video, you’ll get something like this

<video>
    <source type="video/mp4" src="blob:https://x.com/805458aa-96b8-4157-8ca7-ef909a831075">
</video>

I tried to open the source url it in the browser (without blob:) but that leads to a page not found

Hmm...this page doesn’t exist. Try searching for something else.

What is going on here, how does this URL work?