I want to build a website that have video streaming like netflix as my sideproject. I would like to know whether they build their own way the solution for video streaming or they use also webrtc?
Netflix primarily uses DASH (Dynamic Adaptive Streaming over HTTP), but also has some other fallback encoding profiles (depending on platform). As far as I can tell, WebRTC is not used by Netflix.
Wikipedia has some more technical background on Netflix, while a different thread here on StackOverflow sheds some light on advantages and disadvantages of several streaming options.