How does plug.dj or similar sites work?

Question

YouTube

Good afternoon!
Recently wondered how the site plug.dj worked? For those who do not know, this is a service that allows you to create a playlist through youtube that plays like streaming.
For example, when a new user enters a page with a playlist, his video starts playing not from the beginning, but from the place where the current song is left to listen to.
Here I wonder what technologies are needed to implement this.
Thanks in advance for your replies!

Answer 1

there is a whole layer of options on how to do this.
For example, a YouTube playlist can be obtained through their api, such services often have an api, google services api is very functional but complex.
There are a couple of ways to memorize a track.
Write position in cookies\localstore
Send info to server via jax\sockets
Write time in address bar via history api.
Of all the options, sockets seem to me the most beautiful (WebSocket, or Long Polling, or Comet). Sockets will allow you to synchronize one playlist for each user, across devices or browsers, and much more.