The most easiest and simplest Tutorial step by step with free source code: Play YouTube Video using WebView Widget in Android Studio version 3.1.2.
Create new project with Application name: Play YouTube Video; Minimum SDK: API 27 – Android 8.1 (Oreo).
Run app in mobile device or Emulator (API 27 – Android 8.1) and watch video from YouTube in format portrait or landscape.