The Picture-in-picture mode was introduced on Android 8 Oreo, which enables to draw an app over other apps in a small window to offer seamless multi-tasking. However, most of the apps do not support Picture-in-picture mode.
The picture-in-picture mode for YouTube is the most sort out feature on smartphones, which will enable users to play a video in a small window. Few months before the picture-in-picture mode was made available for the YouTube on Android. However, the feature was limited to YouTube Premium subscription (paid YouTube service for ad-free video streaming and exclusive content).
The picture-in-picture mode is natively integrated on the macOS and iOS. For iOS users, YouTube premium users can use the picture-in-picture mode using the native YouTube app. Normal users can open safari on both macOS and iOS to use picture-in-picture mode, which works like a charm.
According to users, the picture-in-picture mode for YouTube is now available for non-YouTube Premium subscribers as well. Users who are running on the latest YouTube version on an Android smartphone with Android 8 Oreo OS can enjoy the same. However, as of now, this feature is limited to the US market and it does not work outside the US (at least in India).
I did change my location from India to the US in the YouTube app, which did not make any difference. It looks like that the update is being rolled out in a phase and as of now, there is no information on this feature coming to India what so ever.
How to user picture-in-picture mode on YouTube?
Go to YouTube app on your smartphone, play a video of your interest.
Press on the home button, voila, you are enjoying your video on a small popup window on the home screen.
Click on the window to maximize the video, which will take you back to the native YouTube app.
However, as of now, there are some restrictions and every video does not support picture in picture mode.
There are a plenty of third-party apps for Android smartphone, which enables picture-in-picture mode on any Android smartphone running on the latest software update. Ex: Musical YouTube like Pixel 2 is one of those apps.