Picture-in-picture currently requires Chrome 68 to work with a number of flags enabled. For now, the feature is implemented as an extension that you click to pop out a video from a web page.
The video pops out into a resizable window which hovers above content on your desktop. You can also minimise the browser window and continue to watch the video.
ChromeUnboxed reported that it has tested the feature on different file formats and found that most standard web video files work with it.
According to the report, the feature is expected to be available for Linux, Mac, Windows, and Chrome OS.