The Picture-in-Picture mode and Split Screen mode are the recent development in Android OS. Xiaomi is preparing to include these two cool features into its Android based MIUI skin. According to latest news, Picture-in-Picture mode and Split Screen mode will be included in the next major release of MIUI. In all probability, both functions will be included in MIUI 9. Redmi/Mi handset users can expect MIUI 9 in this summer (based on previous releases).
The Split Screen feature enables users to run two apps side by side on a single screen. It will work both in landscape and portrait mode. This feature is not a new development. It has been a feature of Samsung and LG phones for years. With Android Nougat, Google refined this feature and made available for Pixel and Nexus phones. Mi/Redmi users can experience this feature soon.
At the same time, Picture-in-Picture (PIP) mode is the latest development in Android. With Android O developer preview, Google introduced Picture-in-Picture (PIP) mode for Android. This feature allows users to separate a video from its player so that it is always viewable while using other apps.
Obviously not all apps will support Split Screen mode and Picture in Picture mode. App developers need to make their applications compatible with these two features. However, it is assumed that all MIUI system apps will support both features.
It is expected that, both functions (Split-Screen and PIP) will be included in the next major release of MIUI ROM. Most probably it will be MIUI 9, which is expected to release in August 2017 (based on the previous release history). (Source)