WhatsApp is constantly experimenting with new things and this time, they are making videos more seamless with your current chat conversations. After opening up WhatsApp file transfer to any file format, the next big thing would be picture-in-picture viewing for both YouTube and video calls.
According to WhatsApp Beta Info, WhatsApp will be supporting YouTube playback within the app itself. So if someone sends over a YouTube link, it will play as a pop-up, which allows you to view it without leaving WhatApp.
At the moment, this is still under development for iOS devices. You can move the video box around or expand it to a bigger size. They noted that the active video can only be played in the same chat room so it will disappear if you switch to another conversation.
For those on Android, WhatsApp is supporting Picture in Picture for video calls with their current Beta. At the moment, it is enabled by default for those who are on Android O. Unlike the YouTube Picture in Picture mode for iOS, it appears that you can maintain the video call across different chat conversations.
Note that these features are still in Beta and it should be rolled out eventually to all users.
