This is a limitation of the YouTube app on Android. It automatically stops video playback as soon as you move it to the background. The same is true for the YouTube mobile website as well. The videos will play as long as the web browser – be it Chrome or some other browser – is in focus. Switch to a different app and the video will pause itself.
The Google Play store has several apps that support background playback thus letting you use YouTube as a music player. I did try them all and here are my favorites.
The STREAM app has a simple interface and minimal features which is what I like most about this app. Just use the search button to find videos and playlists on YouTube and hit the play button. You can also tap and hold a search result to favorite it or to add it to your playlist. STREAM doesn’t link to your YouTube account and all your playlists and favorites are saved locally.
other similar apps are :