WhatsApp has updated the stable version of the app with a couple of features that it added to the beta version a while back. Users can now enjoy PiP video calls and have text-only Status messages. We have already discussed the text-only status message feature before so we will just talk about PiP here. PiP or picture-in-picture mode is a feature of Android Oreo that lets a video element continue to run in a small window even if the main app is minimized. WhatsApp takes advantage of this feature by letting you minimize your video call to a small window if you leave the main app and...
Source: http://www.gsmarena.com/whatsapp_adds_pictureinpicture_support_for_video_calls-news-27174.php