How is video uploading on TikTok implemented?

Question

HTML

Good afternoon everyone.
I noticed that in TikTok, when scrolling, videos are played instantly. The delay occurs only when loading the next "pack" of videos.
How do you think this is implemented?
Are the first few seconds of each video downloaded in one request, then streamed while watching? Or is there a different approach?
Is it possible to implement this in HTML5?

Answer 1

https://developer.mozilla.org/en-US/docs/Web/HTTP/...
https://developer.mozilla.org/en-US/docs/Web/HTML/...