I developed a simple application when playing around with the YouTube API, which allows users to view four channels simultaneously in full screen mode, with individual sound control for each channel.
It uses only html and javascript.
Instructions:
- Copy a Youtube video/live link you want to use.
- Back in app, press Q, W, A or S to paste link in top-left, top-right, bottom-left or bottom-right quadrant respectively.
- You can play four videos simultaneously, moving mouse around the screen will unmute each video when mouse hovers over each player.
- This behaviour can be activated/deactivated pressing M key.
- Responsive design for any screen, there is a tiny gap between four players and screen borders so you can move mouse around without affecting sound.

Repository and live demo:
Github 👉 https://github.com/stabilini/multiple-videos-youtube.git
Live demo 👉 https://stabilini.com/YTchannels/