iPads and Macs have the picture-in-picture feature that allows users to get an overlay of video that they can watch while performing some other task. Sadly this feature is not available on older models of iPad, iPhone and iPod touch devices. If you want to enable this awesome feature on an unsupported device, then you might want to check the ForceInPicture tweak from Cydia. The tweak supports the iOS 10 jailbreak in addition to supporting to iOS 9.
Although you can enable the picture-in-picture on smaller devices like iPhone with this tweak there is a solid reason why Apple chose not to. The smaller screens of these devices does not give a very good viewing experience to the users. It is nice to have the feature on unsupported devices nevertheless. A great thing about this tweak is that it enables the native PiP feature of iOS, which is disabled on certain devices by default, so the performance is definitely better than any third-party created solution. It only works in the default video player of iOS and not in third-party apps. So you might be able to use it with videos playing in Safari but not with apps like Youtube or Vimeo.
To use the picture-in-picture feature after installing ForceInPicture tweak you can simply press the dedicated button that appears when watching the video. Then you have to exit the app by pressing the home button, after which the video will appear as an overlay on the screen. It will have three buttons for pause/play, exit and a button to return to the full screen mode. You can move the video around by dragging on it with one finger.
You can download the ForceInPicture tweak from Cydia for free, where it is available under the BigBoss repo. It currently supports iOS 10 and iOS 9 powered devices.