How it works?

Hi, last day I was thinking about how Netflix, Spotify, Youtube works.
Sometimes when I'm visiting some differents webs I always check and inspect with the DevTools to see what does it have (resources, images, comments in HTML code, tags, ajax calls, what libraries it uses...)
When I visit websites that offer you multimedia content I always find a video tag or source tag with a link attr to the video that is hosted in his own server, and with that link I can access to the video from my browser.
My question is: How netflix, spotify of plattforms like this send videos, music...? Im pretty sure they don't use ajax to send the complete album of ACDC or netflix don't use an iframe to show me the last episode of Breaking bad.