WhatsApp was updated to version 2.17.265 on the beta channel yesterday and as most times, it didn't seem like the new version brought anything new to the table. But it turns out that this isn't the case this time; you just need to be on the newest and hottest version of Android to notice the change. WhatsApp now support picture-in-picture video calls on Android O.
When you start a video call on Android Nougat and below then tap back, the call goes into the background and the video gets paused while the audio continues and you go back to your text conversation and can do other stuff on your phone.Read More
WhatsApp beta adds a picture-in-picture mode for video calls on Android O was written by the awesome team at Android Police.