How vanced youtube is made ? journey of vanced youtube

[devggaurav]

Hello @here, I do not know if I can ask this question here or can discuss this here, but as an android developer, I am very curious to know how such a thing can be achieved, How we can get inside of a system application, and can modify it and even can make a better version of it, I looked for at many places but got no idea, if possible can someone from vacnced team can give an idea to achieve such interesting thing and make this android world better.