I want to play youtube videos in my Android TV APP. I am also working on a Android phone/tablet APP and I was able to use Youtube Android API to play videos. But when I try
The YouTube playback API may not work on Android TV, but you can always implement your own playing mechanism in-app. Take a look at YouTube's web player API: https://developers.google.com/youtube/iframe_api_reference
You can load a WebView in your app and from there add an iframe and JS logic to integrate with your controller.
To interface between your JS and Java code, take a look at a project like this: https://github.com/Fleker/WebGameBridge.js for how to use the WebView APIs.
In terms of getting data, there are also web APIs for this that you can access through your WebView.